#include <iostream>
#include <fstream>

using namespace std;

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

#define maxn 5000010

int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;

int main()
{
      f >> N >> K;
      int i;
      for (i = 1; i <= N; i++)
      {
            f >> A[i];
      }
      f.close();
      Front = 1;
      Back = 0;
      for (i = 1; i <= N; i++)
      {
            while (Front <= Back && A[i] <= A[Deque[Back]])
                  Back--;
            Deque[++Back] = i;
            if (Deque[Front] == i - K)
                  Front++;
            if (i >= K)
                  Sum += A[Deque[Front]];
      }
      g << Sum;
      g.close();
      return 0;
}