#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;
const int N = 1010,M = 10010;
int h[N],e[M],ne[M],pot[N][N],st[N],idx;
int n,m;

void add(int a,int b){
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx++;
}

int main(){
    memset(h,-1,sizeof h);
    cin >> n >> m;
    for(int i = 0;i < m;i++){
        int a,b;
        cin >> a >> b;
        add(a,b);
    }

    for(int i = 1;i <= n;i++){
        queue<int> q;
        memset(st,0,sizeof st);
        q.push(i);st[i] = 1;
        while(q.size()){
            int t = q.front();
            q.pop();

            for(int i = h[t];i != -1;i = ne[i]){
                int k = e[i];
                if(!st[k]) q.push(k);st[k] = 1;
            }
        }
        for(int j = 1;j <= n;j++){
            if(st[j]) pot[i][j] = pot[j][i] = 1;
        }
    }

    int res = 0;
    for(int i = 1;i <= n;i++){
        int flag = 1;
        for(int j = 1;j <= n;j++){
            if(!pot[i][j]){
                flag = 0;
                break;
            }
        }
        if(flag) res++;
    }

    cout << res << endl;
    return 0;
}