#include <iostream>
#include <fstream>
#include <stack>
#include <cstring>
#define vmax 100001
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
struct nod
{
    int y;
    nod *urm;
};
stack<int> s;
nod *lis[vmax],*p;
int n,m,i,j,viz[vmax],nrc=0;

void citire(nod *lis[])
{
    f>>n>>m;
    while(f>>i>>j)
    {
        p = new nod;
        p->y = j;
        p->urm = lis[i];
        lis[i] = p;
    }
}

void dfs(nod *lis[], int start)
{
    viz[start] = 1;
    s.push(start);
    while(!s.empty())
    {
        viz[s.top()] = 1;
        p = lis[s.top()];
        while(p)
        {
            if(!viz[s.top()])
            {
                viz[s.top()] = 1;
                s.push(p->y);
            }
            p=p->urm;
        }
        s.pop();
    }
    nrc++;
}

int main()
{
    citire(lis);
    for(i=1; i<=n; i++)
        if(!viz[i])
            dfs(lis,i);
    g << nrc/2;
    return 0;
}