#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    ll N, M;
    cin >> N >> M;
    vector<vector<ll>> G(N);
    for(ll i = 0; i < M; i++) {
        ll A, B;
        cin >> A >> B;
        A--;
        B--;
        G[B].push_back(A);
    }
    ll ans = 0;
    for(ll i = 0; i < N; i++) {
        if(G[i].size() == 0) ans++;
    }
    cout << ans << endl;
}