1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <cstdlib>
 5 using namespace std;
 6 
 7 #define MAXN 1005
 8 int n, m;
 9 int fa[MAXN];    //父节点
10 int mark[MAXN];
11 
12 void init()
13 {
14     for (int i = 0; i <= n; i++)
15     {
16         fa[i] = i;
17         mark[i] = 0;
18     }
19 }
20 
21 int find(int x)
22 {
23     if (x == fa[x])
24         return x;
25     else
26         return fa[x] = find(fa[x]);
27 }
28 
29 void set_union(int x, int y)
30 {
31     int x1 = find(x);
32     int y1 = find(y);
33 
34     if (x1 == y1)
35         return;
36     if (mark[x1] < mark[y1])
37     {
38         fa[x1] = y1;
39     }
40     else
41         fa[y1] = x1;
42     if (mark[x1] == mark[y1])
43         mark[x1]++;
44 }
45 
46 int main()
47 {
48     while (~scanf("%d",&n))
49     {
50         if (n == 0)
51             break;
52         scanf("%d", &m);
53         init();
54         for (int i = 0; i < m; i++)
55         {
56             int a, b;
57             scanf("%d %d", &a, &b);
58             set_union(a, b);
59         }
60 
61         int ans = 0;
62         for (int i = 1; i <= n; i++)
63         {
64             if (find(i) == i)
65                 ans++;
66         }
67         printf("%d\n", ans - 1);
68     }
69     //system("pause");
70     return 0;
71 }