1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 
 7 int n,m;
 8 int head,tail;
 9 int in; 
10 int sum,ans;
11 int num[300010],pos[300010];
12 
13 int main(){
14     scanf("%d%d",&n,&m);
15     head=1;
16     tail=2;
17     for(int i=1;i<=n;i++){
18         scanf("%d",&in);
19         sum+=in;
20         while(num[tail-1]>=sum&&tail>head) tail--;
21         num[tail]=sum;
22         pos[tail]=i;
23         tail++;
24         while(i-pos[head]>m) head++;
25         ans=max(ans,sum-num[head]);
26     }
27     printf("%d\n",ans);
28     return 0;
29 }