#include <fstream>
#include <queue>

using namespace std;

ifstream cin ("deque.in");
ofstream cout ("deque.out");

const int MaxN = 5000005;

int n, k;
int v[MaxN];
deque <pair <int, int>> dq;

int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) {
    cin >> v[i];
  }

  for (int i = 1; i <= k; ++i) {
    while (dq.size() and dq.back().first > v[i]) {
      dq.pop_back();
    }

    dq.push_back(make_pair(v[i], i));
  }

  long long ans = dq.front().first;

  for (int i = k + 1; i <= n; ++i) {
    while (dq.size() and dq.front().second < i - k + 1) {
      dq.pop_front();
    }

    while (dq.size() and dq.back().first > v[i]) {
      dq.pop_back();
    }

    dq.push_back(make_pair(v[i], i));
    ans += dq.front().first;
  }

  cout << ans << '\n';
  return 0;
}