#include<bits/stdc++.h>
using namespace std;
#define fastio cin.tie(0), cout.tie(0), ios::sync_with_stdio(0);
typedef long long ll;
#define int long long
const int M = 1e5+1;
vector<int> e[M];
int dfn[M], dfc;
int stk[M], top = -1, num;
vector<int> bct[M<<1];
int tarjan(int u){ // return low
dfn[u] = ++dfc;
stk[++top] = u;
int low = dfn[u];
for(const int &v: e[u]){
if(dfn[v]) low = min(low, dfn[v]);
else{
int tmp = tarjan(v);
if(tmp==dfn[u]){
bct[++num].push_back(u);
while(stk[top]!=u) bct[num].push_back(stk[top--]);
for(const int &w: bct[num]) bct[w].push_back(num);
}
else low = min(low, tmp);
}
}
return low;
}
int n;
ll ans = 0;
int tree_dp(int u, int p){
ll sum = 0, cnt = (u<=n);
for(const int &v : bct[u]){
if(v==p) continue;
int tmp = tree_dp(v, u);
sum += cnt*tmp;
cnt += tmp;
}
sum += cnt*(dfc-cnt);
ans += sum*(u>n?(int)bct[u].size():-1);
//cout << u << ' ' << sum << '\n';
return cnt;
}
int main(){
fastio
int m;
cin >> n >> m;
fill(dfn+1, dfn+n+1, 0);
num = n;
for(; m; m--){
int u, v;
cin >> u >> v;
e[u].push_back(v);
e[v].push_back(u);
}
for(int i=1; i<=n; i++) if(!dfn[i] && !e[i].empty()){
dfc = 0, tarjan(i), top--;
/*for(int i=1; i<=num; i++){
cout << i << " :";
for(const int &v: bct[i]) cout << ' ' << v;
cout << '\n';
}*/
tree_dp(i, 0);
}
cout << (ans<<1) << '\n';
return 0;
}
Compilation message
cc1plus: error: '::main' must return 'int'
