#include <cstdio>
#include <vector>

using namespace std;

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

void dfs(int nod)
{
    d[nod] =-1;
    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++)
    {
        scanf("%d %d", &x, &y);
        v[x].push_back(y);
    }
    int nr=0;
    for(int i=1; i<=n; i++)
    {
        if(d[i] != -1)
        {
            dfs(i);
            nr++;
        }
    }
    printf("%d", nr);
    return 0;
}