POJ 1491

#include<iostream>
#include<cmath>
#include<iomanip>
#define MAXN 50
using namespace std;

int _m[MAXN];
int gcd(int a,int b);
int main()
{
//freopen("acm.acm","r",stdin);
int n;
int i;
int j;
double sum_all;
double sum;
while(cin>>n,n)
{
sum = 0;
sum_all = 0;
for(i = 0; i < n; ++ i)
{
cin>>_m[i];
}
for(i = 0; i < n; ++ i)
{
for(j = i+1; j < n; ++ j)
{
if(gcd(_m[i],_m[j]) == 1)
{
++ sum;
}
++ sum_all;
}
}
if(sum == 0)
{
cout<<"No estimate for this data set."<<endl;
continue;
}

cout<<setiosflags(ios::fixed)<<setprecision(6)<<sqrt(((sum_all*6.0)/sum))<<endl;
}

}

int gcd(int a,int b)
{
if(b == 0)
return a;
return gcd(b,a%b);
}