#include <bits/stdc++.h>

 using namespace std;

 const int MAXN=1e6+;

 const int inf=1e9;

 int sum[MAXN], q[MAXN];

 int main(void){

     int n, k;

     while(scanf("%d%d", &n, &k)!=EOF){

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

             int x;

             scanf("%d", &x);

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

         }

         sum[n+]=-inf;

         int ans=, front=, rear=;

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

             ans=max(ans, sum[i]);

             if((front==rear||sum[i]>sum[q[front]])){

                 if(i-q[rear+]+<k){

                     q[++front]=i;

                 }else{

                     while(i-q[rear+]+>=k&&front>rear){

                         rear++;

                     }

                     q[++front]=i;

                 }

             }else if(sum[i]<sum[q[front]]){

                 while(front>rear&&sum[i]<sum[q[front]]){

                     ans=max(ans, sum[q[front]]-sum[q[rear+]]);

                     front--;

                 }

                 while(i-q[rear+]+>=k&&front>rear){

                     rear++;

                 }

                 q[++front]=i;

             }

         }

         printf("%d\n", ans);

     }

     return ;

 }