4 2
1 3
4 3
3 3
1 2
1 3
2 3
5 2
1 2
3 5
999 0
0

1
0
2
998

Hint
Hint
 
Huge input, scanf is recommended.

#include<iostream>
#include<stdio.h>
using namespace std;
int pre[1000];
int find(int r)
{
    while(r!=pre[r])
		r=pre[r];
	return r;
}
void join(int a,int b)
{
	int x,y;
   x=find(a);
   y=find(b);
   if(x!=y)
	   pre[y]=x;
}
int main()
{
	int N,M,a,b,ans,i;
    while(scanf("%d",&N) && N)
	{
		scanf("%d",&M);
	   for(i=1;i<=N;i++)
		  pre[i]=i;
	   ans=0;
	   for(i=1;i<=M;i++)
	   { 
		   scanf("%d%d",&a,&b);
	      join(a,b);
	   }
	   for(i=1;i<=N;i++)
	   {
		   if(pre[i]==i)
			   ans++;
	   }
	   printf("%d\n",ans-1);
	}
	return 0;
}