#include <fstream>
#include <vector>
#define MAX 100010

using namespace std;
ifstream fin ("dfs.in");
ofstream fout ("dfs.out");
int n, m, v[MAX], nr;
vector <int> a[MAX];

void dfs (int nod) {
    v[nod] = 1;
    for (int l = 0; l < a[nod].size(); l++) {
        if (!v[ a[nod][l] ])
            dfs( a[nod][l] );
    }
}

int main()
{
    int i, x, y;
    fin >> n >> m;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        a[x].push_back(y);
    }
    for (i = 1; i <= n; i++) {
        if (!v[i]) {
            dfs(i);
            nr++;
        }
    }
    fout << nr;
    return 0;
}