#include<iostream>
#include<fstream>

using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");

int viz[100005],nod[100005],m,n;

int main ()
{
    int x,y,k=1;
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y;
        if(nod[x] == 0) {
                nod[x]=k;
                ++k;
        }
        if(nod[y] == 0) nod[y]=nod[x];
    }
    for(int i=1;i<=n;++i)
        if(nod[i]==0)++k;
    g<<k-1;

}