#include <iostream>
#include<deque>
#include<fstream>
using namespace std;

long long n,i,x,k,s=0;
deque <int> dq,pq;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");

  f>>n;
  f>>k;
  for(i=1;i<=n;i++)
  {
      f>>x;
      if(!dq.empty()&& pq.front()<=i-k)
      {
          dq.pop_front();
          pq.pop_front();
      }
      while(!dq.empty()&&dq.back()>=x)
      {
          dq.pop_back();
          pq.pop_back();
      }
      pq.push_back(i);
      dq.push_back(x);
      if(i>=k) s=s+dq.front();
  }
  g<<s;
  f.close();
  g.close();
    return 0;
}