#include <iostream>
#include <limits.h>
#include <algorithm>
#include <math.h>
#include <cctype>
#include <cmath>
#include <bits/stdc++.h>
#include <string>
#include <utility>
#include<vector>
#define ll long long
#define ull unsigned long long
#define fixed(n) fixed << setprecision(n)
//#define ceil(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define sz(x) int(x.size())
#define charToInt(s) (s - '0')
#define Num_of_Digits(n) ((int)log10(n) + 1)
#define fi first
#define se second
#define number_line iota(all(vec) , 1)
#define nl "\n"
#define pi 3.14159
#define all(s) s.begin(), s.end()
#define rall(v) v.rbegin() , v.rend()
#define Mod 1'000'000'007
#define INF 2'000'000'000
#define Upper(s) transform(all(s), s.begin(), ::toupper);
#define Lower(s) transform(all(s), s.begin(), ::tolower);
using namespace std;
void esraa()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    // freopen("func.in" , "r" , stdin);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
void solve(){
    ll n , m;
    cin >> n >> m;
    vector < int > vec(n) ;
    for(auto & i : vec) cin >> i;
    ll l = 0 , r = 0;
     deque < char >dq;
    while(r - l + 1 != m){
      dq.emplace_back(vec[r++]);
    }
    ll maxi = LLONG_MIN , sum = 0;
   for( ; r < sz(vec) ; r++){
      dq.emplace_back(vec[r]);
      for(int i = 0 ; i < sz(dq) ; i++){
        sum += (dq[i] * (i + 1));
        maxi = max(maxi , sum);
      }
      sum = 0;
      dq.pop_front();
}
cout << maxi << nl;
}
int main()
{
    esraa();
    int t = 1;
    //cin >> t;
    while(t--)
        solve();
    return 0;
}