#include <stdio.h>
#include <deque>

using namespace std;

deque <int> deck1;
deque <int> deck2;

long long ans;
int N, K;
int nr;

int main() {

  FILE *fin = fopen("deque.in", "r");
  FILE *fout = fopen("deque.out", "w");

  int i, j;

  fscanf(fin, "%d %d", &N, &K);
  for (i = 1; i <= K; i++) {
    fscanf(fin, "%d", &nr);
    while (!deck1.empty() && deck1.back() > nr) {
      deck1.pop_back();
      deck2.pop_back();
    }
    deck1.push_back(nr);
    deck2.push_back(i);
  }

  ans += deck1.front();

  for (i = K + 1; i <= N; i++) {
    fscanf(fin, "%d", &nr);
    while (deck1.back() > nr) {
      deck1.pop_back();
      deck2.pop_back();
    }
    deck1.push_back(nr);
    deck2.push_back(i);

    while (i - deck2.front() + 1 > K) {
      deck1.pop_front();
      deck2.pop_front();
    }

    ans += deck1.front();
  }


  fprintf(fout, "%lld\n", ans);

  return 0;
}