#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: admin
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2116 kb
****************************************************************/