#include <queue>
#include <set>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;
#define LL long long
const int N = 1e4 + 10;
const int INF = 0x3f3f3f3f;
int n,m,fa[N];
int find(int x)
{
	if(fa[x]==x) return x;
	return fa[x]=find(fa[x]);
}
int main()
{
	while(cin>>n&&n)
	{
		cin>>m;
		for(int i=1;i<=n;++i)
			fa[i]=i;
		for(int i=1;i<=m;++i)
		{
			int x,y;
			cin>>x>>y;
			x=find(x),y=find(y);
			fa[x]=y;
		}
		int ans=0;
		for(int i=1;i<=n;++i)
			if(fa[i]==i)
				ans++;
		cout<<ans-1<<endl;
	}
	return 0;
}