#include <bits/stdc++.h>
using namespace std;
#define io {ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);}
 
const int maxN=1e5;
int N,K;
long num[maxN];
 
deque<int> Q;
int main() {
	io
	cin >> N >> K;
	num[0]=0;
	for(int i=1; i<=N; i++){
		cin >> num[i];
		num[i]+=num[i-1];
	}
	Q.push_back(0);
	long ans=0;
	for(int i=1; i<=N; i++){
		if(i-Q.front()>K){
			Q.pop_front();
		}
		while(!Q.empty() and num[Q.back()]>=num[i])
			Q.pop_back();
		Q.push_back(i);
		ans=max(ans,num[i]-num[Q.front()]);
		//cout << num[Q.front()] << ' ' << ans << '\n';
	}
	cout << ans;
}

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MTAgNCAKMSAtNSA3IDIgNSAtMiA2IDMgMCAyIA==

10 4 
1 -5 7 2 5 -2 6 3 0 2