/**
 * @link http://acm.hdu.edu.cn/showproblem.php?pid=1232
 * @author Sycamore
 * @date Aug, 18
 */
import java.util.*;

class Main{
   static int []parent=new int[1000];
   static int find(int x)
   {
      return parent[x]=x==parent[x]?x:find(parent[x]);
   }
   static void Union(int x,int y)
   {
      parent[find(x)]=find
 
(y);
   }
    public static void main(String args[]){
        Scanner scanner=new Scanner(System.in);
        while(scanner.hasNext())
        {
           int n=scanner.nextInt();
           if(n==0)break;
           int m=scanner.nextInt();
           for(int i=1;i<=n;i++)parent[i]=i;
           for(int i
 
=0;i<m;i++)
           {
              int a=scanner.nextInt(),b=scanner.nextInt();
            Union(a,b);
           }
           int cnt=0;
           for(int i=1;i<=n;i++)
              if(parent[i]==i)
                 ++cnt;
           System.out.println(cnt-1);
        }
        scanner.close();
    
 
}
}

HDU 1232: 暢通工程(in Java)