poj1491水题

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
//water
int GCD(int a,int b)
{
    if(a<b)
        swap(a,b);
    return b?GCD(b,a%b):a;
}
int main()
{
    int n;
    int num[55];
    while(scanf("%d",&n),n)
    {
        int cnt = 0;
        for(int i = 0; i<n; ++i)
            scanf("%d",(num+i));
        for(int i = 0; i<n-1; ++i)
        {
            for(int j  = i+1; j<n; ++j)
            {
                if(GCD(num[i],num[j])==1)
                    cnt++;
            }
        }
        if(!cnt)
            puts("No estimate for this data set.");
        else
            printf("%.6f\n",sqrt(3.0*n*(n-1)/(1.0*cnt)));
    }
}