#include <cstdio>
#include <vector>

using namespace std;

const int mxn = 100005;

int n, m, sum;
vector <int> G[mxn];
bool viz[mxn];

void parcurgere(int pos){
    viz[pos] = 1;
    for(vector<int>::iterator it = G[pos].begin(); it != G[pos].end(); ++it)
        if(not viz[*it]){
            parcurgere(*it);
        }
}

inline void dfs(){
    for(int i = 1; i <= n; i++)
        if(not viz[i]){
            sum ++ ;
            parcurgere(i);
        }
}

int main(){
    freopen("dfs.in", "r", stdin);
    freopen("dfs.out", "w", stdout);

    scanf("%d %d", &n, &m);
    for(int i = 0; i < m; i++){
        static int x, y;
        scanf("%d %d", &x, &y);
        G[x].push_back(y);
    }

    dfs();

    printf("%d\n", sum);

    return 0;
}