#include <bits/stdc++.h>

#define NMAX 100001

using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");

int n, m, s, i, x, y, viz[NMAX],comp=1;

vector<int> L[NMAX];

void DFS(int nod)
{
    viz[nod]=comp;
    for(int & cnt : L[nod])
        if(!viz[cnt])
            DFS(cnt);
}

int main() {
    fin >> n >> m ;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        if (x != y)
            L[x].push_back(y);
    }

    for(i=1;i<=n;i++)
    {
        if(!viz[i])
        {
            DFS(i);
            comp++;
        }
    }
    fout<<comp-1;


    return 0;
}