#undef _GLIBCXX_DEBUG #include <bits/stdc++.h> using namespace std; int main() { ios::sync_with_stdio(false); cin.tie(0); int n, m; cin >> n >> m; vector<set<int>> gs(n); for (int i = 0; i < m; i++) { int x, y; cin >> x >> y; x--; y--; gs[x].insert(y); gs[y].insert(x); } long long ans = 0; vector<int> weight(n, 1); set<pair<int,int>> s; for (int i = 0; i < n; i++) { s.emplace(gs[i].size(), i); } while (s.size() > 1) { int i = s.begin()->second; assert(!gs[i].empty()); if (gs[i].size() > 1) { break; } s.erase(s.begin()); int j = *gs[i].begin(); gs[i].clear(); ans += (long long) 2 * weight[i] * (n - weight[i]); weight[j] += weight[i]; auto it = gs[j].find(i); assert(it != gs[j].end()); s.erase({gs[j].size(), j}); gs[j].erase(it); s.emplace(gs[j].size(), j); } if (s.size() == 1) { cout << ans / 2 << '\n'; return 0; } vector<vector<int>> g(n); for (int i = 0; i < n; i++) { g[i] = vector<int>(gs[i].begin(), gs[i].end()); } vector<int> id(n, -1); int cnt = 0; for (int i = 0; i < n; i++) { if ((int) g[i].size() > 2) { id[i] = cnt++; } } if (cnt == 0) { for (int i = 0; i < n; i++) { if ((int) g[i].size() == 2) { id[i] = cnt++; break; } } assert(cnt > 0); } vector<int> rev_id(n, -1); for (int i = 0; i < n; i++) { if (id[i] != -1) { rev_id[id[i]] = i; } } vector<vector<vector<vector<int>>>> edges(cnt, vector<vector<vector<int>>>(cnt)); for (int i = 0; i < n; i++) { if (id[i] >= 0) { for (int j : g[i]) { if (id[j] >= 0) { edges[id[i]][id[j]].emplace_back(); } } } } for (int i = 0; i < n; i++) { if ((int) g[i].size() == 2 && id[i] == -1) { vector<int> edge; edge.push_back(weight[i]); id[i] = -2; vector<int> fin(2); for (int dir = 0; dir < 2; dir++) { int x = g[i][dir]; int px = i; while (id[x] == -1) { assert((int) g[x].size() == 2); edge.push_back(weight[x]); id[x] = -2; int nx = px ^ g[x][0] ^ g[x][1]; px = x; x = nx; } fin[dir] = x; reverse(edge.begin(), edge.end()); } edges[id[fin[1]]][id[fin[0]]].push_back(edge); } } vector<vector<int>> dist(cnt, vector<int>(cnt, n + 1)); for (int i = 0; i < cnt; i++) { dist[i][i] = 0; } for (int i = 0; i < cnt; i++) { for (int j = 0; j < cnt; j++) { for (auto &p : edges[i][j]) { dist[i][j] = dist[j][i] = min(dist[i][j], (int) p.size() + 1); } } } for (int k = 0; k < cnt; k++) { for (int i = 0; i < cnt; i++) { for (int j = 0; j < cnt; j++) { dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]); } } } vector<vector<vector<vector<long long>>>> edge_pref_sum(cnt, vector<vector<vector<long long>>>(cnt)); vector<vector<vector<vector<long long>>>> edge_pref_sum_by_pos(cnt, vector<vector<vector<long long>>>(cnt)); for (int i = 0; i < cnt; i++) { for (int j = 0; j < cnt; j++) { edge_pref_sum[i][j].resize(edges[i][j].size()); edge_pref_sum_by_pos[i][j].resize(edges[i][j].size()); for (int k = 0; k < (int) edges[i][j].size(); k++) { edge_pref_sum[i][j][k].resize(edges[i][j][k].size() + 1); edge_pref_sum_by_pos[i][j][k].resize(edges[i][j][k].size() + 1); for (int t = 0; t < (int) edges[i][j][k].size(); t++) { edge_pref_sum[i][j][k][t + 1] = edge_pref_sum[i][j][k][t] + edges[i][j][k][t]; edge_pref_sum_by_pos[i][j][k][t + 1] = edge_pref_sum_by_pos[i][j][k][t] + (long long) edges[i][j][k][t] * t; } } } } auto get = [&](int i, int j, int k, int from, int to, int coeff_from, int coeff_to) -> long long { if (from > to) { return 0; } assert(0 <= from && to <= (int) edges[i][j][k].size() - 1); long long ret = (edge_pref_sum[i][j][k][to + 1] - edge_pref_sum[i][j][k][from]) * coeff_from; if (coeff_from != coeff_to) { assert(abs(coeff_from - coeff_to) == to - from); long long other = edge_pref_sum_by_pos[i][j][k][to + 1] - edge_pref_sum_by_pos[i][j][k][from]; other -= (edge_pref_sum[i][j][k][to + 1] - edge_pref_sum[i][j][k][from]) * from; ret += other * (coeff_from < coeff_to ? 1 : -1); } return ret; }; for (int v = 0; v < cnt; v++) { long long w = weight[rev_id[v]]; for (int j = 0; j < cnt; j++) { ans += dist[v][j] * w * weight[rev_id[j]]; } for (int i = 0; i < cnt; i++) { for (int j = 0; j < cnt; j++) { for (int k = 0; k < (int) edges[i][j].size(); k++) { int x = dist[v][i]; int y = dist[v][j]; int cc = (y - x + (int) edges[i][j][k].size() + 1) / 2; cc = min(max(cc, 0), (int) edges[i][j][k].size()); ans += w * get(i, j, k, 0, cc - 1, x + 1, x + cc); ans += w * get(i, j, k, cc, (int) edges[i][j][k].size() - 1, y + ((int) edges[i][j][k].size() - cc), y + 1); } } } } vector<pair<int,int>> pairs; for (int i = 0; i < cnt; i++) { for (int j = 0; j < cnt; j++) { if (!edges[i][j].empty()) { pairs.emplace_back(i, j); } } } for (int ii = 0; ii < cnt; ii++) { for (int jj = 0; jj < cnt; jj++) { for (int kk = 0; kk < (int) edges[ii][jj].size(); kk++) { for (int tt = 0; tt < (int) edges[ii][jj][kk].size(); tt++) { long long w = edges[ii][jj][kk][tt]; for (int i = 0; i < cnt; i++) { int d1 = dist[ii][i] + tt + 1; int d2 = dist[jj][i] + (int) edges[ii][jj][kk].size() - tt; ans += w * weight[rev_id[i]] * min(d1, d2); } for (auto &p : pairs) { int i = p.first; int j = p.second; for (int k = 0; k < (int) edges[i][j].size(); k++) { if (i == ii && j == jj && k == kk) { int d1 = tt; int d2 = (int) edges[ii][jj][kk].size() - tt + dist[i][j] + 1; if (d1 <= d2) { ans += w * get(i, j, k, 0, tt, tt, 0); } else { int cut = (d1 - d2 + 1) / 2; ans += w * get(i, j, k, 0, cut - 1, d2, d2 + cut - 1); ans += w * get(i, j, k, cut, tt, tt - cut, 0); } int d3 = (int) edges[ii][jj][kk].size() - 1 - tt; int d4 = tt + 1 + dist[i][j] + 1; if (d3 <= d4) { ans += w * get(i, j, k, tt, (int) edges[i][j][k].size() - 1, 0, (int) edges[i][j][k].size() - 1 - tt); } else { int cut = (d3 - d4 + 1) / 2; ans += w * get(i, j, k, (int) edges[i][j][k].size() - cut, (int) edges[i][j][k].size() - 1, d4 + cut - 1, d4); ans += w * get(i, j, k, tt, (int) edges[i][j][k].size() - 1 - cut, 0, (int) edges[i][j][k].size() - 1 - cut - tt); } } else { int d1 = dist[ii][i] + tt + 1; int d2 = dist[jj][i] + (int) edges[ii][jj][kk].size() - tt; int d3 = dist[ii][j] + tt + 1; int d4 = dist[jj][j] + (int) edges[ii][jj][kk].size() - tt; int x = min(d1, d2); int y = min(d3, d4); int cc = (y - x + (int) edges[i][j][k].size() + 1) / 2; cc = min(max(cc, 0), (int) edges[i][j][k].size()); ans += w * get(i, j, k, 0, cc - 1, x + 1, x + cc); ans += w * get(i, j, k, cc, (int) edges[i][j][k].size() - 1, y + ((int) edges[i][j][k].size() - cc), y + 1); } } } } } } } assert(ans % 2 == 0); cout << ans / 2 << '\n'; return 0; }