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

using namespace std;

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

vector<vector<int>> v;
bool check[100010];
int n, m, ans;

void DFS(int val)
{
    check[val] = 1;

    for(int i = 0; i < v[val].size(); i++)
        if(!check[v[val][i]])
            DFS(v[val][i]);
}

int main()
{
    in >> n >> m;

    v.resize(n + 5);

    for(int i = 0; i < m; i++)
    {
        int x, y;
        in >> x >> y;

        v[x].push_back(y);
    }

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

    out << ans << '\n';

    return 0;
}