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

vector <int> v[100005];
int n, m;
int d[100005];

void dfs(int nod)
{
    d[nod]=0;
    for(auto vecin:v[nod])
    {
        if(d[vecin]==-1)
        {
            dfs(vecin);
        }
    }


}

int main() {

    freopen("dfs.in", "r", stdin);
    freopen("dfs.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for(int i=1;i<=m;i++)
    {
        int x, y;
        scanf("%d %d", &x ,&y);
        v[x].push_back(y);
    }

    for(int i=1;i<=n;i++)
        d[i]=-1;

    int nr=0;

    for(int i=1;i<=n;i++)
    {
        if(d[i]==-1)
        {
            dfs(i);
            nr++;
        }

    }
    printf("%d", nr);

    return 0;
}