#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;

int n,m,conexe;
char vizitat[100001];


struct nod
{
    int val;
    struct nod *urm;
};

struct nod *vecini[100001];

void dfs(int nod)
{
    struct nod *p;
    p=vecini[nod];
    while(p){

       if(vizitat[p->val]!='1'){ vizitat[p->val]='1'; dfs(p->val); }
p=p->urm;
    }
}


int main()
{
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
struct nod *a;
int dim=sizeof(struct nod);
int x,y;
for(int i=1; i<=m; i++)
{
scanf("%d %d",&x,&y);

a=(struct nod*)malloc(dim);
a->urm=vecini[x];
a->val=y;
vecini[x]=a;
}

for(int i=1; i<=n; i++)

    if(vizitat[i]!='1'){ conexe++; vizitat[i]='1'; dfs(i);  }
printf("%d",conexe);

    return 0;
}