#include<bits/stdc++.h>
using namespace std;
int n,m,lead[1010];
bool vis[1010];
struct edge{
	int from;
	int to;
}e[10010];
int main()
{
	while(scanf("%d%d",&n,&m)!=EOF)
	{
		int ans=-1;
		memset(vis,false,sizeof(vis));
		for(int i=1;i<=n;i++)
			lead[i]=i;
		for(int i=1;i<=m;i++)
		{
			int f,t;
			cin>>f>>t;
			e[i].from=f;
			e[i].to=t;
			if(lead[f]!=lead[t])
			{
				int tmp=lead[f];
				lead[f]=lead[t];
				for(int j=1;j<=n;j++)
					if(lead[j]==lead[f])
						lead[j]=lead[t];
			}
		}
		for(int i=1;i<=n;i++)
			if(!vis[lead[i]])
			{
				vis[lead[i]]=true;
				ans++;
			}
		cout<<ans<<endl;
	}
	return 0;
}