#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 5;
std::vector <int> G[MAXN];
int comp ;
bool seen[MAXN];
void dfs(int node){
    seen[node] = 1;
    for(auto x: G[node]){
        if(!seen[x])
            dfs(x);
    }
}
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int main()
{
    int n, m;
    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        int x, y;
        fin >> x >> y;
        G[x].push_back(y);
    }
    for(int i = 1; i <= n; ++i){
        if(!seen[i]) comp++, dfs(i);
    }
    fout << comp;
    return 0;
}