#include <vector>
#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("dfs.in");
ofstream out("dfs.out");
vector <int> v[100001],x;
int n,m;
void citire()
{
    int i,a,b;
    in>>n>>m;
    for(i=1;i<=m;i++)
    {
        in>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
}
void declarare_x()
{
    int i;
    for(i=0;i<=n;i++)
        x.push_back(0);
    x[0]=999;
}
int nod_nevizitat()
{
    int i;
    for(i=1;i<=n;i++)
        if(x[i]==0)
            return i;
    return 0;
}
void adancime(int pl,int y)
{
    int i,j;
    x[pl]=y;
    for(i=0;i<v[pl].size();i++)
        if(x[v[pl][i]]==0)
            adancime(v[pl][i],y);

}
int main()
{
    int i,y=0;
    declarare_x();
    citire();
    declarare_x();
    while(nod_nevizitat()!=0)
    {
        y++;
        adancime(nod_nevizitat(),y);
    }
    out<<y;

    return 0;

}