#include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <cmath>

 #include <algorithm>

 using namespace std;

 typedef long long int64;

 const double eps=1e-;

 const int maxn=;

 int n,a[maxn],sum[maxn],pos[maxn];

 double l,r,mid,ans,b[maxn],s[maxn],list[maxn];

 int64 k;

 int lowbit(int x){return x&(-x);}

 void insert(int x){for (int i=x;i<=n+;i+=lowbit(i)) sum[i]++;}

 int64 query(int x){

     int64 temp=;

     for (int i=x;i;i-=lowbit(i)) temp+=sum[i];

     return temp;

 }

 bool judge(double num){

     memset(sum,,sizeof(sum)); b[]=;

     for (int i=;i<=n;i++) b[i]=a[i]-num;

     for (int i=;i<=n;i++) s[i]=s[i-]+b[i],list[i]=s[i];

     list[n+]=; sort(list+,list+n+);

     for (int i=;i<=n;i++) pos[i]=lower_bound(list+,list+n+,s[i])-list;

     pos[]=lower_bound(list+,list+n+,)-list;

     int64 tot=;

     insert(pos[]);

     for (int i=;i<=n;i++) tot+=query(pos[i]),insert(pos[i]);

     return tot>=k;

 }

 int main(){

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

     for (int i=;i<=n;i++) scanf("%d",&a[i]);

     l=1.0,r=100000.0;

     while (l+eps<r){

         mid=(l+r)/2.0;

         if (judge(mid)) l=mid;

         else r=mid;

     }

     printf("%.4lf\n",l);

     return ;

 }