#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

vector < int > v[100002];
bitset < 100002 > mark;

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

int main()
{
    ifstream f("dfs.in");
    ofstream g("dfs.out");
    int n, m, ans = 0;
    f >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        f >> x >> y;
        v[x].push_back(y);
    }

    for(int i = 1; i <= n; i++)
        if(!mark[i])
        {
            ans++;
            dfs(i);
        }

    g << ans << '\n';
    f.close();
    g.close();
    return 0;
}