#include <bits/stdc++.h>
using namespace std;

const int maxn = 10001;
int N, M;

int p[maxn];
int cnt[maxn];
int ans;
int ffind(int x)
{
    return p[x] == x? x : p[x] = ffind(p[x]);
}

void init(int n)
{
    ans = 1;
    for(int i = 1; i <= n ; i++)
        p[i] = i, cnt[i] = 1;

}

void uunion(int u, int v)
{
    int a = ffind(u);
    int b = ffind(v);
    if(a != b)
        p[b] = a, cnt[a] += cnt[b], cnt[b] = 0;
}


int main()
{
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r",stdin);
    freopen("out.txt", "w",stdout);
#endif // ONLINE_JUDGE

    while(~scanf("%d %d", &N, &M) && N)
    {
        init(N);
        int a,b;
        for(int i = 0; i < M; i++)
        {
            scanf("%d%d", &a, &b);
            uunion(a,b);
        }
        int num = 0;

        for(int i = 1; i <= N; i++)
        {
           // printf("cnt[%d]: %d", i , cnt[i]);
            if(cnt[i] != 0) num++;
        }

        printf("%d\n", num - 1);
    }
    return 0;
}