#include <bits/stdc++.h>

using namespace std;

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

const int nMax = 100005;
int n, m, ans;
vector <int> L[nMax];
bool viz[nMax];

inline void Read()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        L[x].push_back(y);
    }
}

inline void Dfs(int nod)
{
    viz[nod] = true;
    for(auto it : L[nod])
        if(!viz[it])
            Dfs(it);
}

inline void Solve()
{
    int ans = 0;
    for(int i = 1; i <= n; i++)
        if(!viz[i])
            ans++, Dfs(i);
    fout << ans << "\n";
}

int main()
{
    Read();
    Solve();
    fin.close();fout.close();
    return 0;
}