#include<iostream>

#include<cstdio>

#include<algorithm>

#include<cmath>

#include<cstring>

#include<string>

#include<cstdlib>

#include<stack>

#include<vector>

#include<queue>

#include<deque>

#include<map>

#include<set>

using namespace std;

#define lck_max(a,b) ((a)>(b)?(a):(b))

#define lck_min(a,b) ((a)<(b)?(a):(b))

typedef long long LL;

const int maxn=1e7+;

LL N,L;

double a[maxn],b[maxn],sum[maxn];

inline double resd() {double ls;scanf("%lf",&ls);return ls;}

inline LL read()

{

    LL kr=,xs=;char ls;

    ls=getchar();

    while(!isdigit(ls))

    {

        if(!(ls^))

            kr=-;

        ls=getchar();

    }

    while(isdigit(ls))

    {

        xs=(xs<<)+(xs<<)+(ls^);

        ls=getchar();

    }

    return xs*kr;

}

int main()

{

    N=read();L=read();

    for(LL i=;i<=N;i++) a[i]=resd();

    double l=-1e6,r=1e6,eps=1e-;

    while(r-l>eps)

    {

        double mid=(l+r)/;

        for(LL i=;i<=N;i++) b[i]=a[i]-mid;

        for(LL i=;i<=N;i++) sum[i]=sum[i-]+b[i];

        double maxx=-1e10,minn=1e10;

        for(LL i=L;i<=N;i++)

            minn=lck_min(minn,sum[i-L]),maxx=lck_max(maxx,sum[i]-minn);

        if(maxx>=) l=mid;

        else r=mid;

    }

    printf("%lld\n",LL(r*));

return ;

}