> #include<iostream>
> #include<math.h>
> #include<iomanip>
> #include<string.h>
> using namespace std;
> //int a[50];
> inline bool com(int a,int b)
> {
>        int t;
>        if(a<b){t=a;a=b;b=t;}
>        while(b)
>        {t=a%b;a=b;b=t;}
>        if(a>1)return 1;
>        else return 0;
> }
> int main()
> {
>     int n;
>     while(cin>>n&&n)
>     {
>            //memset(a,0,50);
>            int *a = new int[n];
> 	       for(int i=0;i<n;i++)
>            cin>>a[i];
>            int count=0;
>            for(int i=0;i<n-1;i++) 
>              for(int j=i+1;j<n;j++) 
>                  if(!com(a[i],a[j]))count++;
>            if(count==0)cout<<"No estimate for this data set."<<endl;
>            else cout<<setiosflags(ios::fixed)<<setprecision(6)<<sqrt(3.0*n*(n-1)/count)<<endl;//改为3.0   OK
>            delete []a;   
>               
>     }
>     
>     return 0;
> }