#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int dq[5000001];
int v[10001];
int main()
{
  int st=0,dr=-1,n,k,s;
  for(int i=0;i<n;i++)
  {
      if(st<=dr && dq[st]==i-k)
      {
          st++;
      }
      while(st<=dr && v[i]<=v[dq[dr]])
      {
          dr--;
      }
      dq[++dr]=i;
      if(i>=k-1)
      {
          s+=v[dq[st]];
      }
  }
  cout<<s;
  return 0;
}