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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,K; cin >> N >> K;
    priority_queue<long long,vector<long long>,greater<>> Q;
    long long answer = 0,now = 0;
    vector<long long> A(K);
    for(auto &a : A) cin >> a;
    
    for(int i=K-1; i>=0; i--){
        now += A.at(i)*(i+1);
        if(i < K-1) A.at(i) += A.at(i+1);
        if(i) Q.push(A.at(i));
    }

    answer = now;
    long long zero = 0;
    for(int i=K; i<N; i++){
        long long a; cin >> a;
        now += a*K;
        if(Q.size()) now += zero-Q.top(),Q.pop();
        answer = max(answer,now);
        if(K > 1) Q.push(zero),zero -= a;
    }
    cout << answer << endl;
}