# include <cstdio>
# include <vector>
using namespace std;

FILE *f = freopen("dfs.in", "r", stdin);
FILE *g = freopen("dfs.out", "w", stdout);

const int N_MAX = 100010;

int nr, n, m;
vector <int> G[N_MAX];
bool viz[N_MAX];

void read(){

    scanf("%d %d", &n, &m);

    for (int i=1; i<=m; i++){
        int x ,y;

        scanf("%d %d", &x, &y);
        G[x].push_back(y);
    }
}

void dfs(int node){
    viz[node] = true;

    for (int vecin : G[node]){
        if (!viz[vecin])
            dfs(vecin);
    }
}

void solve(){
    for (int i=1; i<=n; i++){
        if (!viz[i]){
            nr ++;
            dfs(i);
        }
    }
}

void write(){
    printf("%d\n", nr);
}

int main(){
    read();
    solve();
    write();
    return 0;
}