1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 int n, m;
 6 int par[1010];
 7 int road[1010];
 8 
 9 //经过路径压缩后的并查集
10 int find(int x)
11 {
12     return par[x] == x ? x : par[x] = find(par[x]);
13 }
14 void merge(int x, int y)
15 {
16     x = find(x);
17     y = find(y);
18     if(x != y)
19     {
20         par[x] = y;
21     }
22 
23 }
24 int main()
25 {
26     int a, b;
27     while(scanf("%d %d", &n, &m) != EOF && n)
28     {
29         int ans = 0;
30         for(int i = 1; i <= n; i++)
31         {
32             par[i] = i;    
33         }
34         for(int i = 1; i <= m; i++)
35         {
36             scanf("%d %d", &a, &b);
37             merge(a, b);    //归并所有有关联的节点
38         }
39         memset(road, 0, sizeof(road));
40         for(int i = 1; i <= n; i++)    //遍历所有的节点，查找根节点
41         {
42             road[find(i)] = 1;
43         }
44         for(int i = 1;i <= n; i++)    //统计根节点数目
45         {
46             if(road[i])
47             {
48                 ans++;
49             }
50         }
51         printf("%d\n", ans-1);    //合并到一个节点上，要-1
52     }
53 }