#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 5 * 1e6 + 1e2;

int n, k;

int v[NMAX];
int dq[NMAX];

int le = 1;
int ri;

long long res;

void go_left(int pos) {
  if(pos - dq[le] == k)
    le++;
}

void go_right(int pos) {
  while(le <= ri && v[pos] <= v[dq[ri]])
    ri--;

  dq[++ri] = pos;
}

int main()
{
  in >> n >> k;

  for(int i = 1; i <= n; i++) {
    in >> v[i];

    go_left(i);
    go_right(i);

    if(i >= k)
      res += v[dq[le]];
  }

  out << res << '\n';


  in.close();
  out.close();

  return 0;
}