#include <bits/stdc++.h>

using namespace std;
int n, i, st, dr, x, c, minn = INT_MAX, l, k, s[100000001];
int main()
{
     ifstream f("deque.in");
     ofstream g("deque.out");
     cin >> n >> k;
     for(i = 1; i <= n; i ++)
     {
        f >> s[i];
     }
     st = 1;
     dr = n;
     while(st <= dr)
     {
         i = st;
         c = 1;
         minn = INT_MAX;
         while(c <= k)
         {
             if(minn > s[i])
                minn = s[i];
             i ++;
             c ++;
         }
         l = l + minn;
         st ++;
     }
     g << l;
}