#include<bits/stdc++.h>
using namespace std;

int n,m;
bool con1[1005][1005] = {false};
bool con2[21005][1005] = {false};
bool vis[1005] = {false};
vector<int> dep[1005];


int iscon1(int x,int y){
	if(con1[x][y]==true) return 1;
	for(int i = 0;i < dep[x].size();i++){
		if(vis[dep[x][i]]==false){
			vis[dep[x][i]] = true;
			if(iscon1(dep[x][i],y)==1)
			return 1;
		}

	}
	return 0;
}

int iscon2(int x,int y){
	if(con2[y][x]==true) return 1;
	for(int i = 0;i < dep[x].size();i++){
		if(vis[dep[x][i]]==false){
			vis[dep[x][i]] = true;
			if(iscon2(dep[x][i],y)==1)
			return 1;
		}

	}
	return 0;
}




int main(){
	int a,b,ans = 0;
	scanf("%d%d",&n,&m);
	for(int i = 0;i < m;i++){
		scanf("%d%d",&a,&b);
		dep[a].push_back(b);
	}
	for(int i = 1;i <= n;i++){
		con1[i][i] = con2[i][i] =  true;
	}
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= n;j++){
			if(iscon1(i,j)==1){
				fill(vis,vis+1005,false);
				con1[i][j] = true;
			}
			else if(iscon2(j,i)==1){
				fill(vis,vis+1005,false);
				con2[i][j] = true;
			}
			else{
				fill(vis,vis+1005,false);
				goto L;
			}
		}
		ans++;
		L:;
	}
	printf("%d",ans);
}
/*
4 4
1 2
1 3
2 4
3 4
2 1
*/