#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
int n,m,a[110][110],a1,a2,b[110][110],ans=0;
bool bk[110];
void dfs1(int p){
	bk[p]=1;
	for(int i=1;i<=n;i++)if(a[p][i]&&!bk[i])dfs1(i);
	return;
}
void dfs2(int p){
	bk[p]=1;
	for(int i=1;i<=n;i++)if(b[p][i]&&!bk[i])dfs2(i);
	return;
}
int main(){
	freopen("contest.in","r",stdin); 
	freopen("contest.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
    	scanf("%d%d",&a1,&a2);
    	a[a1][a2]=1;
    	b[a2][a1]=1;
    }
    for(int i=1;i<=n;i++){
    	memset(bk,0,sizeof(bk));
    	dfs1(i);
    	dfs2(i);
    	int ju=1;
    	for(int j=1;j<=n;j++)if(!bk[j]){ju=0;break;}
        if(ju)++ans;
	}
    printf("%d",ans);
	return 0;
}