#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
bool cmp(int a,int b){
	return a>b;
}
int main(){
	int n,d;
	int bottle[1000006];
	cin>>n;
	cin>>d;
	for(int i=1;i<=n;i++){
		cin>>bottle[i];
	}
	int zh[1000006],max;
	for(int i=1;i<=n-d;i++){
		for(int j=i;j<=i+d;j++){
			zh[i]+=bottle[j];
		if(max<zh[i]){
			max=zh[i];
		}
	}
	cout<<max;
	return 0;
}