#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <limits>
#include <numeric>
#include <vector>


int main() {
  using usize = std::size_t;
  using u64 = std::uint64_t;

  static constexpr u64 inf = std::numeric_limits<u64>::max();

  usize n, k;
  std::cin >> n >> k;

  u64 ans = inf;

  std::vector<u64> a(n);
  for (auto &e : a) {
    std::cin >> e;
  }

  std::vector<u64> pmin(n), smin(n);
  pmin[k - 1] = a[k - 1];
  for (usize i = k; i != n; ++i) {
    pmin[i] = std::min(pmin[i - 1], a[i]);
  }
  smin[n - 1] = a[n - 1];
  for (usize i = n; i != k;) {
    i -= 1;
    smin[i - 1] = std::min(smin[i], a[i - 1]);
  }

  std::vector<usize> b(n - (k - 1));
  std::iota(b.begin(), b.end(), k - 1);
  std::sort(b.begin(), b.end(), [&](usize l, usize r) { return a[l] < a[r]; });

  std::vector<usize> bmi = b, bma = b;
  bmi.insert(bmi.begin(), n);
  bma.insert(bma.begin(), 0);
  for (usize i = 0; i != b.size(); ++i) {
    bmi[i + 1] = std::min(bmi[i], b[i]);
    bma[i + 1] = std::max(bma[i], b[i]);
  }

  u64 sum = 0;

  for (usize i = 1; i * k <= n; ++i) {
    sum += a[b[i - 1]];
    if (i == 1) {
      ans = std::min(ans, a[k - 1]);
      continue;
    }
    if (bmi[i] <= (k - 1) * i) {
      if (bma[i] >= k * i - 1) {
        ans = std::min(ans, sum);
      } else {
        u64 t = a[b[i - 1]];
        if (bmi[i - 1] > (k - 1) * i) {
          t = a[b[i - 2]];
        }
        ans = std::min(ans, sum - t + smin[k * i - 1]);
      }
    } else {
      if (bma[i] >= k * i - 1) {
        u64 t = a[b[i - 1]];
        if (bma[i - 1] < k * i - 1) {
          t = a[b[i - 2]];
        }
        ans = std::min(ans, sum - t + pmin[(k - 1) * i]);
      } else {
        u64 t = a[b[i - 1]] + a[b[i - 2]];
        ans = std::min(ans, sum - t + pmin[(k - 1) * i] + smin[k * i - 1]);
      }
    }
  }

  std::cout << ans << "\n";

  return 0;
}