#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
const int MAXM=200005;
const int MAXN=100005;
queue<int>Q;
struct NODE{
	int to,next;
}Edge[MAXM];
int Len,N,M;
int Head[MAXN],Sum[MAXN],IN[MAXN],OUT[MAXN];
bool Flag[MAXN];

void Add_edge(int x,int y){
	Len++; Edge[Len].to=y; Edge[Len].next=Head[x]; Head[x]=Len;
}

void Init(){
	scanf("%d%d",&N,&M);
	int a,b;
	for(int i=1;i<=M;i++){
		scanf("%d%d",&a,&b);
		Add_edge(a,b);
		IN[b]++; OUT[a]++;
	}
}

int DFS(int x){
	if(Flag[x])return Sum[x];
	Flag[x]=true;
	if(OUT[x] == 0){
		Sum[x]=1; return 1;
	}
	for(int i=Head[x];i;i=Edge[i].next){
		int y=Edge[i].to;
		Sum[x]+=DFS(y);
	}
	return Sum[x];
}

int main(){
	freopen("chain_2016.in","r",stdin);
	freopen("chain_2016.out","w",stdout);
	Init();
	int ans=0;
	for(int i=1;i<=N;i++)
		if(IN[i] == 0 && OUT[i] != 0)
		ans+=DFS(i);
	printf("%d\n",ans);
}