#include <bits/stdc++.h>

using namespace std;

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

#define N_MAX 5000000

deque <int> seq;
int v[N_MAX];

int main() {
  int n, k, i;
  long long int sum;

  fin >> n >> k;
  for(i = 0; i < n; ++i) {
    fin >> v[i];
  }
  fin.close();

  sum = 0;
  for(i = 0; i < n; ++i) {
    while(!seq.empty() && v[i] <= v[seq.front()]) {
      seq.pop_front();
    }

    while(!seq.empty() && seq.back() <= i - k) {
      seq.pop_back();
    }

    seq.push_front(i);


    if(i >= k - 1) {
      sum += 1LL * v[seq.back()];
    }
  }

  fout << sum << '\n';

  fout.close();

  return 0;
}