1 #include<bits/stdc++.h>
 2 using namespace std;
 3 int n,m;
 4 int pre[1001];
 5 int r[1001];
 6 int findset(int x) {
 7     int r=x;
 8     while(pre[r]!=r) r=pre[r];
 9     int i=x,j;
10     // 路径压缩 
11     while(i!=r) {
12         j=pre[i];
13         pre[i]=r;
14         i=j;
15     }
16     return r;
17 }
18 void join(int x,int y) {
19     int f1=findset(x),f2=findset(y);
20     // 按秩合并 
21     if(r[f1]<=r[f2]) {
22         pre[f1]=f2;
23         if (r[f1]==r[f2]) r[f2]++;
24     }
25     else pre[f2]=f1;
26 }
27 int main() {
28     while(~scanf("%d",&n)&&n) {
29         scanf("%d",&m);
30         int ans=0;    
31         memset(pre,0,sizeof(pre));
32         memset(r,0,sizeof(r));
33         for (int i=1;i<=n;++i) pre[i]=i;
34         for (int i=1;i<=m;++i) {
35             int x,y;
36             scanf("%d%d",&x,&y);
37             join(x,y);
38         }
39         for (int i=1;i<=n;++i)
40             if(pre[i]==i) ans++;
41         printf("%d\n",ans-1);
42     }
43 }