1 #include <cstdio>
 2 int n,m;
 3 int pre[1005];
 4 void init(){
 5     for (int i=1; i<=n; i++) {
 6         pre[i]=i;
 7     }
 8 }
 9 int find(int x){
10     int r=x;
11     while (pre[x]!=x) {
12         x=pre[x];
13     }
14     pre[r]=x;
15     return x;
16 }
17 void join(int x,int y){
18     int fx=find(x),fy=find(y);
19     if(fx!=fy){
20         pre[fx]=fy;
21     }
22 }
23 int main(){
24     while (scanf("%d",&n)!=EOF && n) {
25         int res=-1; //当只有一个连通块时，不需要修路，所以res初始化为-1
26         init();
27         scanf("%d",&m);
28         for (int i=0; i<m; i++) {
29             int a,b;
30             scanf("%d%d",&a,&b);
31             join(a, b);
32         }
33         for (int i=1; i<=n; i++) {
34             if(pre[i]==i)   res++;
35         }
36         printf("%d\n",res);
37     }
38     return 0;
39 }