#include<iostream.h>
#include<fstream.h>
ifstream f("dfs.in");
ofstream g("dfs.out");
int i,viz[50],a[1000][1000],nr=1,n,m;

void citire(){
	int i,j,k;
	f>>n>>m;
		while (f>>i>>j)
		a[i][j]=a[j][i]=1;
	
}

void df(int x){
	int i;
	viz[x]=nr;
	for (i=1;i<=n;i++)
		if (a[i][x] && !viz[i])
			df(i);
}
int main(){
	citire();
	for (i=1;i<=n;i++)
		if (!viz[i])
		{
					nr++;
			df(i);

		}
		g<<nr-1;

		return 0;
}