#include<stdio.h>#include<string.h>#include<iostream>using namespace std;#define MAXN 10005 struct Node{ int to,next;}edge1[MAXN*5],edge2[MAXN*5];int head1[MAXN];int head2[MAXN];int mark1[MAXN],mark2[MAXN];int tot1,tot2;int cnt1,cnt2,st[MAXN],belong[MAXN];int num,setNum[MAXN];struct Edge{ int l,r;}e[MAXN*5];void add(int a,int b){ edge1[tot1].to=b;edge1[tot1].next=head1[a];head1[a]=tot1++; edge2[tot2].to=a;edge2[tot2].next=head2[b];head2[b]=tot2++; } void DFS1(int x){ mark1[x]=1; for(int i=head1[x];i!=-1;i=edge1[i].next) if(!mark1[edge1[i].to]) DFS1(edge1[i].to); st[cnt1++]=x; } void DFS2(int x){ mark2[x]=1; num++; belong[x]=cnt2; for(int i=head2[x];i!=-1;i=edge2[i].next) if(!mark2[edge2[i].to]) DFS2(edge2[i].to);} int main(){ int n,m; while(scanf("%d%d",&n,&m)!=EOF) { tot1=tot2=1; for(int i=1;i<=n;i++) { head1[i]=head2[i]=-1; mark1[i]=mark2[i]=0; } for(int i=1;i<=m;i++) { int w,v; scanf("%d%d",&w,&v); e[i].l=w;e[i].r=v; add(w,v); } cnt1=cnt2=1; for(int i=1;i<=n;i++) { if(!mark1[i])DFS1(i); } for(int i=cnt1-1;i>=1;i--) { if(!mark2[st[i]]) { num=0; DFS2(st[i]); setNum[cnt2++]=num; } } int cnt=0; for(int i=1;i<cnt2;i++) if(setNum[i]>=2)cnt++; printf("%dn",cnt); } return 0;}
