#include <fstream>
#include <deque>

std::ifstream fin("deque.in");
std::ofstream fout("deque.out");

std::deque<long int> d;
long int n, k;
long long sum;

inline long int min_element()
{
    int mini = d[0];
    for (int i = 1; i < k; ++i)
    {
        if (d[i] < mini) mini = d[i];
    }
    return mini;
}

inline void citire()
{
    long int aux;
    fin >> n >> k;
    for (int i = 0; i < n; ++i)
    {
         fin >> aux;
         d.push_back(aux);
         if (i >= k - 1)
         {
            sum += min_element();
         }
         if (i >= k - 1)
         {
             d.pop_front();
         }
    }
}

int main()
{
    citire();
    fout << sum;

      return 0;
}