#include <stdio.h>
#include <bitset>
#include <vector>
#define NMAX 100005

using namespace std;

vector<int> v[NMAX];
bitset <NMAX> viz;

void dfs(int i){
    viz[i] = 1;
    for(vector<int> :: iterator it = v[i].begin(); it != v[i].end(); ++it)
        if(!viz[*it])
            dfs(*it);

}

int main(){
    freopen("dfs.in", "r", stdin);
    freopen("dfs.out", "w", stdout);
    int N, M, nr = 0, x, y;
    scanf("%d %d", &N, &M);
    for(int i = 1; i <= M; ++i){
        scanf("%d %d", &x, &y);
        v[x].push_back(y);
    }
    for(int i = 1; i <= N; ++i)
        if(!viz[i]){
            dfs(i);
            ++nr;
        }
    printf("%d\n", nr);
    return 0;
}