#include <stdio.h>
#include <vector>
#include <stack>
#define dim 100000
using namespace std;

vector <int> a[dim];
stack <int> s;
bool v[dim];
int n,cmp;
long long m;

void dfs()
{
    unsigned int i,nod = s.top();
    v[nod] = true; //mark as visited
    for(i=0;i<a[nod].size();i++)
    {
        if (v[a[nod][i]]==false)
        {
            s.push(a[nod][i]);
            dfs();
        }

    }
    s.pop();
}


int main()
{
    int x1,x2;
    long long i;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %lld",&n,&m);
    for (i=0;i<m;i++)
    {
        scanf("%d %d",&x1,&x2);
        a[x1-1].push_back(x2-1);
    }
    for (i=0;i<n;i++)
    {
        if (v[i]==false)
        {
            s.push(i);
            dfs();
            cmp++;
        }
    }
    printf("%d",cmp);
    return 0;
}