#include <bits/stdc++.h>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n, m, x, y, v[100001], cnt;
vector<int> g[100001];

void dfs(int nod){
    v[nod] = cnt;
    for(int i=0; i<g[nod].size(); i++){
        int dest = g[nod][i];
        if(!v[dest]) dfs(dest);
    }
}

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