圆方树orz，参见猫的课件（apio和wc的）以及这里那里
#include <iostream>
#include <cstdio>
using namespace std;
typedef long long ll;
int n, m, uu, vv, oea[100005], loo[100005], dfn[100005], idx, sta[100005];
int siz[200005], val[200005], tot, sze, din, ont, cnt, hea[200005];
ll ans;
struct Edge{
int too, nxt;
}odge[400005], edge[400005];
void add_odge(int fro, int too){
odge[++ont].nxt = oea[fro];
odge[ont].too = too;
oea[fro] = ont;
}
void add_edge(int fro, int too){
edge[++cnt].nxt = hea[fro];
edge[cnt].too = too;
hea[fro] = cnt;
}
void tarjan(int x){
dfn[x] = loo[x] = ++idx;
sta[++din] = x;
siz[x] = 1;
val[x] = -1;
for(int i=oea[x]; i; i=odge[i].nxt){
int t=odge[i].too;
if(!dfn[t]){
tarjan(t);
loo[x] = min(loo[x], loo[t]);
if(loo[t]>=dfn[x]){
int p;
tot++;
add_edge(x, tot);
do{
p = sta[din--];
val[tot]++;
add_edge(tot, p);
siz[tot] += siz[p];
}while(p!=t);
val[tot]++; siz[x] += siz[tot];
}
}
else loo[x] = min(loo[x], dfn[t]);
}
}
void dfs(int x){
if(x<=n) ans += (ll)val[x] * (sze - 1);
ans += (ll)val[x] * (sze - siz[x]) * siz[x];
for(int i=hea[x]; i; i=edge[i].nxt){
int t=edge[i].too;
dfs(t);
ans += (ll)val[x] * (sze - siz[t]) * siz[t];
}
}
int main(){
cin>>n>>m;
tot = n;
for(int i=1; i<=m; i++){
scanf("%d %d", &uu, &vv);
add_odge(uu, vv);
add_odge(vv, uu);
}
for(int i=1; i<=n; i++)
if(!dfn[i]){
tarjan(i);
sze = siz[i];
dfs(i);
}
cout<<ans<<endl;
return 0;
}
