#include <bits/stdc++.h>

std::ifstream fin("dfs.in");
std::ofstream fout("dfs.out");

int n, m;
std::vector<std::vector<int>> arce;
std::vector<bool> v;

void DFS(int start) {
    v[start] = 1;

    for(int i : arce[start]) {
        if(v[i] == 0) {
            v[i] = 1;
            DFS(i);
        }
    }
}

int main() {
    fin >> n >> m;
    arce.resize(n + 1);
    v.resize(n + 1);

    for(int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        arce[x].push_back(y);
    }

    int conexe = 0;
    for(int i = 1; i <= n; ++i) {
        if(v[i] == 0) {
            ++conexe;
            DFS(i);
        }
    }

    fout << conexe;
    return 0;
}