#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>> G(n);
	rep(i, m) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		G[b].push_back(a);
	}
	int ans = 0;
	rep(i, n) {
		if (G[i].size() == 0) ans++;
	}
	cout << ans << endl;
	return 0;
}