#include<bits/stdc++.h>

 using namespace std;

 const int MX = ;

 double dp[MX];

 int x[MX];

 int main(){

     int T,n,k;

     scanf("%d",&T);

     for(int cas=;cas<=T;cas++){

         memset(dp,,sizeof(dp));

         scanf("%d%d",&n,&k);

         int a=,b;

         double sum1=,sum2=;

         for(int i=;i<n;i++) {

             scanf("%d",&x[i]);

             if(x[i]>) {sum1+=x[i];a++;}

             else sum2+=abs(x[i]);

         }

         if(a==){

             printf("Case %d: -1\n",cas);

             continue;

         }

         b=n-a;

         if(a) sum1/=a;

         if(b) sum2/=b;

         k=min(k,b);

         dp[k]=sum1+(b-k)*sum2/a;

         for(int i=k-;i>=;i--){

             dp[i]=(dp[i+]+sum2)*(b-i);

             dp[i]+=sum1*a;

             dp[i]/=n-i;

         }

         printf("Case %d: %.7f\n",cas,dp[]);

     }

     return ;

 }