#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<vector>
#include<queue>
#include<algorithm>
#include<string>
#include<sstream>
#include<cctype>
#include<cmath>
#include<iomanip>
#include<map>
#include<stack>
#include<set>
#include<functional>
#define in(x) x=read()
#define qr read()
#define int ll
#define mp make_pair
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
namespace fastIO
{
    #define BUF_SIZE 100000
    bool IOerror=0;
    inline char nc()
	{
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if (p1==pend){
            p1=buf; pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if (pend==p1){IOerror=1;return -1;}
        }
        return *p1++;
    }
    inline bool blank(char ch){return ch==' '||ch=='\n'||ch=='\r'||ch=='\t';}
    inline ll read()
	{
        bool sign=0; char ch=nc();ll x=0;
        for (;blank(ch);ch=nc());
        if (IOerror)return 0;
        if (ch=='-')sign=1,ch=nc();
        for (;ch>='0'&&ch<='9';ch=nc())x=x*10+ch-'0';
        if (sign)x=-x;
        return x;
    }
    #undef BUF_SIZE
};
using namespace fastIO;
int a[1000010];
double f[3010][3010];
int n,m;
double dfs(int x,int y)
{
	// cout<<x<<' '<<y<<'\n';
	if(f[x][y]>0)return f[x][y];
	if(x>n)return 0;
	if(!y)return f[x][y]=dfs(x+1,y)+a[x];
	double w1=dfs(x+1,y-1),w2=dfs(x+1,y);
	//w1+x w2+a[x]-x
	if(w1>=w2+a[x])return f[x][y]=w2+a[x];
	else return f[x][y]=(w1+w2+a[x])/2;
}
signed main()
{
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	n=qr,m=qr;
	for(int i=1;i<=n;i++)in(a[i]);
	sort(a+1,a+1+n);
	printf("%.6f",dfs(1,m));
	return 0;
}