#include<bits/stdc++.h>
#define u using namespace std;
#define ll long long
#define s scanf
#define p printf
#define f for
u
ll n,k,a[1000005],ans = 0,cnt;
int main(){
	s("%ld\n%ld",&n,&k);
	f(ll i = 0;i<n;i++)s("%ld",&a[i]);
	f(ll i = 0;i<n-k;i++){
		cnt = 0;
		f(ll j = i;j<=i+k;j++){
			cnt+=a[j];
		}
		if(cnt>ans)ans = cnt;
	}
	p("%ld",ans);
	return 0;
}