uva : 412 - Pi

#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<cmath>
using namespace std;

int divisor(int n, int m)
{
   int c;
   while(n%m!=0)
   {
       c=n%m;
       n=m;
       m=c;
   }
    return m;
}

int main()
{
    int n;
    while(scanf("%d",&n)==1&&n!=0)
    {
        int a[n+1],i,j,k,l=0,m=0,npairs=0;
        for(i=0;i<n;i++)scanf("%d",&a[i]);
        for(i=0;i<n;i++)
        {
            for(j=i+1;j<n;j++)
            {
                l=divisor(a[i],a[j]);
                npairs++;
                if(l==1)
                {
                    m++;
                }
            }
        }
        if(m==0)printf("No estimate for this data set.\n");
        else
        {
            double expected_pi = sqrt(6*npairs/(double)m);
            printf("%lf\n",expected_pi);
        }
    }
    return 0;
}