#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
int n,m,a[110][110]={0},ans=0;
int main()
{
	freopen("contest.in","r",stdin);
	freopen("contest.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;++i)
		for(int j=1;j<=n;++j)
			a[i][j]=9999999;
	for(int i=1;i<=m;++i)
	{
		int t1,t2;
		scanf("%d%d",&t1,&t2);
		a[t1][t2]=1;
		//a[t2][t1]=1;
	}
	for(int k=1;k<=n;++k)
		for(int i=1;i<=n;++i)
			for(int j=1;j<=n;++j)
				if(a[i][j]>a[i][k]+a[k][j])
					a[i][j]=a[i][k]+a[k][j];
	/*
	for(int i=1;i<=n;++i)
	{
		for(int j=1;j<=n;++j)
			printf("%d ",a[i][j]);
		printf("\n");
	}
	*/
	for(int i=1;i<=n;++i)
	{
		int t1=0;
		for(int j=1;j<=n;++j)
			if(a[i][j]!=9999999||a[j][i]!=9999999)
				++t1;
		if(t1==n-1)
			++ans;
	}
	printf("%d\n",ans);
	return 0;
}