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

int main()
{
	int N, M;
	cin >> N >> M;
	vector<int> in( N );
	for( int i = 0; i < M; i++ ) {
		int A, B;
		cin >> A >> B;
		B--;
		in[B]++;
	}
	int ans = 0;
	for( int i = 0; i < N; i++ ) {
		if( in[i] == 0 ) ans++;
	}

	cout << ans << endl;
}