#include <bits/stdc++.h>

using namespace std;

ifstream in("ctc.in");
ofstream out("ctc.out");

vector<int> vn[100002], vt[100002];
bool viz[100002];
stack<int> parcurgere;

void dfs (int v) {
    viz[v] = true;
    for (auto vec : vn[v]) {
        if (!viz[vec]) {
            dfs(vec);
        }
    }
    parcurgere.push(v);
}

void dfst (int v) {
    viz[v] = true;
    for (auto vec : vt[v]) {
        if (!viz[vec]) {
            dfst(vec);
        }
    }
}

int main () {

    int n, m;
    in >> n >> m;
    for (int i = 0; i < m; ++i) {
        int a, b;
        in >> a >> b;
        vn[a].push_back(b);
        vt[b].push_back(a);
    }

    for (int i = 1; i <= n; ++i) {
        if (!viz[i]) {
            dfs(i);
        }
    }
    fill(viz, viz + n + 1, false);
    int C = 0;
    while (!parcurgere.empty()) {
        int nod = parcurgere.top();
        parcurgere.pop();
        if (!viz[nod]) {
            dfst(nod);
            C++;
        }
    }
    out << C;
}