HDU 1232

#include<stdio.h>
int father[1005],depth[1005];
void init()
{
    int i;
    for(i = 1; i < 1005;i ++)
    {
        father[i] = i;
        depth[i] = 0;
    }
}

int find(int x)
{
    if(x==father[x])
        return x;
    else
        return father[x] = find(father[x]); 　　//优化树的高度；
}

void unit(int x,int y)
{
    x = find(x);
    y = find(y);
    if(x==y)
        return ;
    if(depth[x]<depth[y])　　　　//注意树的优化，防止高度过高而超时；
    {
        father[x] = father[y];

    }
    else
    {
        if(depth[x]>depth[y])
            father[y] = father[x];
        else
        {
            father[x] = father[y];
            depth[y]++;
        }
    }
}

int main()
{
    int n,m,a,b,j,gr;
    while(~scanf("%d%d",&n,&m)&&n!=0)
    {
        gr = 0;
        init();
        while(m--)
        {
            scanf("%d%d",&a,&b);
            unit(a,b);
        }
        for(j = 1;j <= n;j ++)
        {
            if(j==father[j])
                gr++;
        }
        printf("%d\n",gr-1);
    }
    return 0;
}