#include <cstdio>
#include <string>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
using namespace std;
const int M = 8005;
#define db double
int read()
{
	int x=0,f=1;char c;
	while((c=getchar())<'0' || c>'9') {if(c=='-') f=-1;}
	while(c>='0' && c<='9') {x=(x<<3)+(x<<1)+(c^48);c=getchar();}
	return x*f;
}
//

//
int n,m,w,a[M],h[M],s[M],g[M][20],p[M];db f[M][20];
struct node{db x,y;}q[M];
db slope(node a,node b)
{
	return (a.y-b.y)/(a.x-b.x);
}
Decimal calc(int i,int j)
{
	if(!j) return h[1];
	return (calc(g[i][j],j-1)+s[i]-s[g[i][j]])/(i-g[i][j]+1);
}
signed main()
{
	n=read();m=read();w=read();
	h[1]=read();int k=1;
	for(int i=2;i<=n;i++)
	{
		int x=read();
		if(x>=h[1]) h[++k]=x;
	}
	n=k;m=min(m,n);k=min(m,14);sort(h+1,h+1+n);
	for(int i=1;i<=n;i++)
		f[i][0]=h[1],s[i]=s[i-1]+h[i];
	for(int j=1;j<=k;j++)
	{
		int l=1,r=1;p[1]=1;
		for(int i=1;i<=n;i++)
			q[i]=node{i-1,s[i]-f[i][j-1]};
		for(int i=2;i<=n;i++)
		{
			node u={i,s[i]};
			while(l<r && slope(u,q[p[l]])
				<slope(u,q[p[l+1]])) l++;
			g[i][j]=p[l];
			f[i][j]=(f[p[l]][j-1]+s[i]-s[p[l]])/(i-p[l]+1);
			while(l<r && slope(q[p[r-1]],q[p[r]])
				>slope(q[p[r]],q[i])) r--;
			p[++r]=i;
		}
	}
	int o=n-m+k,u=0;
	for(int i=0;i<=k;i++)
		if(f[o][i]>f[o][u]) u=i;
	Decimal ans=calc(o,u);
	for(int i=o+1;i<=n;i++)
		ans=(ans+h[i])/2;
	cout<<ans.to_string(w<<1)<<endl;
}