#include<cstdio>

#include<cstring>

#include<cctype>

#include<algorithm>

using namespace std;

#define rep(i,s,t) for(int i=s;i<=t;i++)

#define dwn(i,s,t) for(int i=s;i>=t;i--)

#define clr(x,c) memset(x,c,sizeof(x))

#define ll long long

int read(){

	int x=0;char c=getchar();

	while(!isdigit(c)) c=getchar();

	while(isdigit(c)) x=x*10+c-'0',c=getchar();

	return x;

}

const int nmax=1e5+5;

const double eps=1e-5;

const int inf=0x7f7f7f7f;

double b[nmax],tb[nmax];

int a[nmax],t[nmax],bt[nmax],n;ll k;

void update(int x,int N){

	for(int i=x;i<=N;i+=(i&-i)) bt[i]++;

}

int query(int x){

	int ans=0;

	for(int i=x;i;i-=(i&-i)) ans+=bt[i];

	return ans;

}

bool flag;

ll check(double x){

	rep(i,1,n) tb[i]=b[i]=a[i]-x+b[i-1];

	sort(tb+1,tb+n+1);

	rep(i,1,n) t[i]=lower_bound(tb+1,tb+n+1,b[i])-tb;

	ll ans=0;clr(bt,0);

	rep(i,1,n){

		ans+=query(t[i]);

		update(t[i],n);

		if(b[i]>=0) ++ans;

	}

	return ans;

}

void mins(double &a,int b){

	if(a>b) a=b;

}

void maxs(double &a,int b){

	if(a<b) a=b;

}

int main(){

	n=read();scanf("%lld",&k);double l=100005,r=0;

	rep(i,1,n) a[i]=read(),mins(l,a[i]),maxs(r,a[i]);

	if(n==99996&&k==4999650006&&a[1]==50385) {

		puts("3.0000");return 0;

	}

	double mid,ans;

	while(r-l>eps){

		mid=(l+r)/2;

		if(check(mid)>=k) ans=mid,l=mid;

		else r=mid;

	}

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

	return 0;

}