66求调，帮者必关

#include<bits/stdc++.h>
using namespace std;
long long n,m,a[500005],s[500005],ans = 0;
int main(){
	cin>>n>>m;
	for(int i = 1;i<=n;i++){
		cin>>a[i];
		s[i] = s[i-1]+a[i];
		for(int j = 1;j<=m and i-j>=0;j++){
			ans = max(ans,s[i]-s[i-j]);
		}
	}
	cout<<ans;
}