#include<bits/stdc++.h>

using namespace std;

const int maxn = 3e5+;

int a[maxn];

int sum[maxn];

int q[maxn];

int main(){

    int n,k;

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

    a[]=sum[]=;

    for(int i=;i<=n;i++){

        scanf("%d",&a[i]);

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

    }

    int l,r;

    l=r=;

    int ans=-;

    q[]=;

    for(int i=;i<=n;i++){

        while(l<=r&&q[l]<i-k) l++;

        ans=max(ans,sum[i]-sum[q[l]]);

        while(l<=r&&sum[q[r]]>=sum[i]) r--;

        q[++r]=i;

    }

    cout<<ans<<endl;

}