#include <iostream>
#include <fstream>
#include <deque>
std::ifstream fin("deque.in");
std::ofstream fout("deque.out");

int n,k;
int v[5005000];
int pos;
std::deque<int> deq;
long long sum;

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