#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ul unsigned long long

ll mod = 1e9+7;
const int N = 1e6+5;
int MOD = 998244353;
int bit[200000];
int n, k;
ll pref[N];
ll ma[N];
int a[N];
ll kq = 0;
int main() {
	//freopen("CSBN.INP", "r", stdin);
	//freopen("CSBN.OUT", "w", stdout);
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);


	cin >> n >> k;
	pref[0]=0;
	for(int i = 1 ; i <= n ; i++){
		cin >> a[i];
        pref[i] = pref[i - 1] + a[i];
		
	}
	
	for(int i = k;i <= n;i+=1){
		ma[i] = max(ma[i-1],pref[i] - pref[i-k]);
	}
	for (int i = n ; i >= k; i--){
		kq = max(kq, (pref[i] - pref[i-k]) + ma[i - k]);
	}
	cout << kq << "\n";
	
}