#include <bits/stdc++.h>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");

const int N_MAX = 100000;
vector<int> v[N_MAX + 1];
bool fr[N_MAX + 1];
int n;

void dfs(int i) {
    fr[i] = 1;
    for (auto x : v[i]) {
        if (!fr[x]) {
                dfs(x);
        }
    }
}

int main() {
    fin.tie(0);
    std::ios_base::sync_with_stdio(0);
    int m, cnt = 0;
    fin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
    }
    for (int i = 1; i <= n; ++i) {
        if (!fr[i]) {
            dfs(i);
            ++cnt;
        }
    }
    fout << cnt;
}