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| #include<bits/stdc++.h>
#define pb push_back
using namespace std;
const int N=1e5+5,M=3e5+5;
int n,m,d[N];
vector<int> G[N],C[N];
int col,low[N],dfn[N],tot,st[N],top;
int num[N];
void Tarjan(int cur,int rt){
dfn[cur]=low[cur]=++tot;
st[++top]=cur;
for (int i=0;i<(int)G[cur].size();++i){
int to=G[cur][i];
if (!dfn[to]) Tarjan(to,rt),low[cur]=min(low[cur],low[to]);
else if (dfn[to]>=rt) low[cur]=min(low[cur],dfn[to]);
}
if (low[cur]==dfn[cur]){
++col;
while (st[top+1]!=cur) num[st[top]]=col,C[col].pb(st[top--]);
}
}
signed main(){
cin>>n>>m;
if (n==1) return puts("1.000000"),0;
for (int i=1;i<=m;++i){
int x,y;
cin>>x>>y;
G[x].pb(y);
}
for (int i=1;i<=n;++i){
if (!dfn[i]) Tarjan(i,tot+1);
}
for (int i=1;i<=col;++i){
for (int j=0;j<(int)C[i].size();++j){
int cur=C[i][j];
for (int k=0;k<(int)G[cur].size();++k){
int to=G[cur][k];
if (num[to]!=num[cur]) ++d[num[to]];
}
}
}
int ans=0;bool tag=0;
for (int i=1;i<=col;++i){
if (!d[i]){
if (C[i].size()==1&&!tag){
bool flag=0;
int cur=C[i][0];
for (int j=0;j<(int)G[cur].size();++j){
int to=G[cur][j];
if (d[num[to]]==1){
flag=1;break;
}
}
if (!flag) tag=1;
}
++ans;
}
}
if (ans>1&&tag) --ans;
double res=1.0-(double)ans/n;
printf("%.6lf",res);
return 0;
}
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