#include <bits/stdc++.h>
using namespace std;
   
int a[10000],n,i,j,x,s = 0;
int main(){
    cin>>n>>x;
    for(i = 0;i < n;i++){
        cin>>a[i];
    }
       
    sort(a,a+n);
       
    for(i = x;i < n - x;i++){
        s = s + a[i];
    }
    double v = s * 1.0 / (n - x * 2);
    cout<<fixed<<setprecision(1)<<v<<endl; 
}
/**************************************************************
	Problem: 1473
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2116 kb
****************************************************************/