#include <iostream>
#include <fstream>
#include <deque>

std::deque<std::pair<int, int>> dq;

int main() {
  std::ifstream in("deque.in");
  std::ofstream out("deque.out");

  int n, k, a;
  int64_t s = 0;
  in >> n >> k;

  for (int i = 1; i <= n; ++i) {
    in >> a;

    while (!dq.empty() && dq.back().first > a)
      dq.pop_back();

    dq.emplace_back(a, i);

    if (dq.front().second <= i - k)
      dq.pop_front();

    if (i >= k)
      s += dq.front().first;
  }

  out << s;

  return 0;
}