#include<bits/stdc++.h>
#include<cstdio>
#include<iostream>
#include<cstring>
#include<vector>
using namespace std;
const int maxn=100001;
int n,m,ans;
vector<int>G[maxn];
int in[maxn],out[maxn];
int d[maxn];
int dfs(int cur){
	if(!out[cur])d[cur]=1;
	if(d[cur])return d[cur];
	int l=G[cur].size();
	int p=0;
	for(int i=0;i<l;i++){
		p+=dfs(G[cur][i]);
	}
	return d[cur]=p;
}
int main(){
	freopen("chain_2016.in","r",stdin);
	freopen("chain_2016.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		int x,y;
		scanf("%d%d",&x,&y);
		G[x].push_back(y);
		in[y]++;
		out[x]++;
	}
	for(int i=1;i<=n;i++)
	//cout<<in[i]<<" "<<out[i]<<endl;
	if(!in[i]&&out[i])ans+=dfs(i);
	
	
	    
	printf("%d\n",ans);
	return 0;
}