#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n, k;
    cin >> n >> k;
    vector<long long> c(n);
    for (int i = 0; i < n; i++)
        cin >> c[i];

    if (k == 0)
    {
        long long S = c[0];
        for (int i = 1; i < n; i++)
            S += c[i];
        cout << S << endl;
    }  
    else
    {
        vector<int> b(n);
        
        long long S = 0;
        // choose the most right bulb that lights it
        
        for (int i = 0; i < n; i++)
        {
            bool Dark = true;
            for (int j = i - k; j <= i + k; j++)
                if (0 <= j && j < n && b[j] == 1)
                Dark = false;
            if (!Dark)    
                continue;
            // choosing the bulb
            int i0 = i+k;
            if (i0 >= n)
                i0 = n - 1;
            
            for (int j = i + k; j >= i - k; j--)                
                if (n > j && j >=0 &&   c[j] > c[i0])
                    i0 = j;
            S += c[i0];
            b[i0] = 1; 
        }
        
        cout << S << endl;
    }
        
    
    
    return 0;
}