// File Name: 191-E.cpp

// Author: Zlbing

// Created Time: 2013年08月03日 星期六 15时10分13秒

#include<iostream>

#include<string>

#include<algorithm>

#include<cstdlib>

#include<cstdio>

#include<set>

#include<map>

#include<vector>

#include<cstring>

#include<stack>

#include<cmath>

#include<queue>

using namespace std;

#define CL(x,v); memset(x,v,sizeof(x));

#define INF 0x3f3f3f3f

#define LL long long

#define REP(i,r,n) for(int i=r;i<=n;i++)

#define RREP(i,n,r) for(int i=n;i>=r;i--)

const int MAXN=1e5+;

int tree[MAXN];

int n;

int lowbit(int x)

{

    return x&(-x);

}

void add(int pos,int val)

{

    while(pos<=n)

    {

        tree[pos]+=val;

        pos+=lowbit(pos);

    }

}

int read(int x)

{

    int s=;

    while(x>)

    {

        s+=tree[x];

        x-=lowbit(x);

    }

    return s;

}

LL sum[MAXN];

LL num[MAXN];

int N;

LL M;

LL solve(LL mid)

{

    CL(tree,);

    LL ans=;

    for(int i=;i<=N;i++)

    {

        if(sum[i]>=mid)ans++;

        LL t=sum[i]-mid;

        int a=upper_bound(num+,num+n+,t)-num-;

        int b=lower_bound(num+,num+n+,sum[i])-num;

        ans+=read(a);

        add(b,);

    }

    //cout<<"ans="<<ans<<endl;

    return ans;

}

int main()

{

    while(~scanf("%d%lld",&N,&M))

    {

        sum[]=;

        LL l,r;

        REP(i,,N)

        {

            scanf("%lld",&sum[i]);

            sum[i]+=sum[i-];

            num[i]=sum[i];

        }

        sort(num+,num+N+);

        n=unique(num+,num+N+)-num-;

            //cout<<"l="<<l<<"r="<<r<<endl;

        LL best=-;

        l=-1e18;

        r=1e18;

        while(l<=r)

        {

            LL mid=l+(r-l+)/;

            //cout<<"l="<<l<<"r="<<r<<"mid="<<mid<<endl;

            if(solve(mid)>=M)

            {

                best=mid;

                l=mid+;

            }

            else r=mid-;

        }

        cout<<best<<endl;

    }

    return ;

}