#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b, int mod=M) {
    int x = 1;
    a %= mod;
    while (b) {
        if (b & 1) x = (x * a) % mod; 
        a = (a * a) % mod;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************

// 6 4
// -3 4 3 -5 2 4


vector<int> a;

int consistency(int n, int k){
	
	deque<int> up;
	vector<int> prefix(n+1, 0);
	
	int ans = 0;
	
	for(int i=1; i<=n; i++){
		prefix[i] = prefix[i-1] + a[i-1];
		
		while(!up.empty() && prefix[i-1] < prefix[up.back()]  ) up.pop_back();
		up.push_back(i-1);
		
		if(!up.empty() && i-k-1 == up.front()) up.pop_front();
		
		
		auto mini = prefix[up.front()];
		int val = prefix[i] - mini;
		
		ans = max(ans, val);
	}
	
	return ans;
}















int practice(int n, int k){


    return 0;
}





void solve() {
    
    int n, k;
    cin>> n >> k;
    
    a.resize(n);
    for(int i=0; i<n; i++) cin >> a[i];
    
    cout << consistency(n, k) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}