#include <bits/stdc++.h>
#define maxv 100005
using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");
int n,m,ap[maxv];
vector<int>lista[maxv];
void citire()
{
    in>>n>>m;
    int x,y;
    for(int i=1;i<=m;i++)
    {
        in>>x>>y;
        lista[x].push_back(y);
    }
}
void dfs(int node)
{
    ap[node]=1;
    for(auto x:lista[node])
    {
        if(ap[x]==0)
            dfs(x);
    }
}
int main()
{
    int k=0;
    citire();
    for(int i=1;i<=n;i++)
        if(ap[i]==0)
        {
            k++;
            dfs(i);
        }
    out<<k;
    return 0;
}