#include <stdio.h>
int const N=100001;
int vf[N],urm[N],lst[N],nr,viz[N];

void addEdge(int x,int y)
{
    ++nr;
    vf[nr] = y;
    urm[nr] = lst[x];
    lst[x] = nr;
}

void dfs(int x)
{
    viz[x] = true;
    x = lst[x];
    while(x != 0)
    {
        int y = vf[x];
        if(!viz[y]) dfs(y);
        x = urm[x];
    }
}

int main()
{
    int n,m,i,x,y,comp=0;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(i=1;i<=m;i++)
    {
        scanf("%d %d",&x,&y);
        addEdge(x,y);
    }
    for(i=1;i<=n;i++)
    {
       if(!viz[i])
       {
           comp++;
           dfs(i);
       }
    }
    printf("%d",comp);
    return 0;
}