畅通工程//并查集

#include <iostream>

int Find(int a[], int x)
{
    while(x != a[x])
        x = a[x];
    return x;
}

bool IsConnected(int a[], int x, int y)
{
    return Find(a,x) == Find(a,y);
}

void Union(int a[], int x, int y, int& num)
{
    int r1 = Find(a,x);
    int r2 = Find(a,y);
    a[r1] = r2;
    num--;
}

int main()
{
    using namespace std;
    int N=1, M;
    while(1)
    {
        cin >> N;
        if(N == 0)
            return 0;
        cin >> M;
        int * a = new int[N+1];
        for(int i = 0; i < N+1; i++)
            a[i] = i;
        int num = N-1;
        int x, y;
        while(M--)
        {
            cin >> x >> y;
            if(IsConnected(a,x,y))
                continue;
            Union(a,x,y,num);
        }
        printf("%d\n", num);
        delete[] a;
    }
}