#include <bits/stdc++.h>

using namespace std;

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

deque<int>dq;
int n, sum, x, v[5000002], l;

int main()
{
  fin >> n >> l;
  for (int i = 1; i <= l; i++) {
    fin >> v[i];
    while (!dq.empty() && v[dq.back()] > v[i])
      dq.pop_back();
    dq.push_back(i);
  }
  sum = v[dq.front()];
  for (int i = l + 1; i <= n; i++) {
    fin >> v[i];
    while (!dq.empty() && dq.front() < i - l + 1)
      dq.pop_front();
     while (!dq.empty() && v[dq.back()] > v[i])
      dq.pop_back();
    dq.push_back(i);
    sum += v[dq.front()];
  }
  fout << sum;
  return 0;
}