#include <fstream>

using namespace std;

ifstream f ("deque.in");
ofstream g ("deque.out");

int n, k, i, v[5000001], minim = 99999999, pozmin;
long long suma;

int main()
{
 f >> n >> k;
  for (i=1; i<=n; i++)
      f >> v[i];
 int st, dr;
 st = 1, dr = k;
  for (i=st; i<=dr; i++)
     {
         if (v[i] < minim)
         {
            minim = v[i];
            pozmin = i;
         }
     }
  suma = minim;
   while (dr <= n)
   {
       st ++;
       dr ++;
        if (st-1 == pozmin)
        {
            minim = 999999999;
             for (i=st; i<=dr; i++)
                if (v[i] < minim)
             {
                   minim = v[i];
                   pozmin = i;
             }
           suma += minim;
        }
        else {
            if (v[dr] < minim)
            {
                minim = v[dr];
                pozmin = dr;
            }
          suma += minim;
        }
   }
 g << suma;
    return 0;
}