村村通

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000;
// 并查集
int fa[MAXN + 5];
int cnt[MAXN + 5];
int findFa(int x)
{
    if (fa[x] == x)
        return x;
    return fa[x] = findFa(fa[x]);
}
// ---------
int n, m;
int main()
{
    while (cin >> n)
    {
        if (n == 0)
            break;
        cin >> m;
        // 并查集初始化
        for (int i = 1; i <= n; i++)
            fa[i] = i;
        // 处理 m 组关系
        for (int i = 1; i <= m; i++)
        {
            int u, v;
            cin >> u >> v;
            int faU = findFa(u);
            int faV = findFa(v);
            if (faU != faV)
                fa[faU] = faV;
        }
        // 计算答案
        int ans = 0;
        for (int i = 1; i <= n; i++)
            if (fa[i] == i)
                ans++;
        cout << ans - 1 << "\n";
    }
    return 0;
}