#include <iostream>
#include <cstdio>
#define Nmax 1001
using namespace std;
int n,i,j,cmp=0;
int a[Nmax][Nmax];
bool viz[Nmax];
void citire(int &n)
{
    int m;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    int x,y;
    for(i=1;i<=m;++i)
    {
        scanf("%d %d",&x,&y);
        a

    [y]=1;

        a[y]

    =1;

    }
}
void dfs(int x)
{
    viz

    =1;

    for(i=1;i<=n;++i)
     if (!viz && a

    ) dfs(i);

}
int main()
{
    citire(n);
    for(i=1;i<=n;++i)
     if (!viz[i]) {++cmp;dfs(i);}
    printf("%d",cmp);
    return 0;
}