#include <bits/stdc++.h>
#define Nmax 5000010
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int a[Nmax],Deque[Nmax],n,k;
long long sum;

int main()
{
  f>>n>>k;
  for(int i=1;i<=n;++i)
    f>>a[i];

  int f=1,b=0;

  for(int i=1;i<=n;++i)
  {
      while(f<=b && a[i]<=a[Deque[b]]) b--;

      Deque[++b]=i;

      if(Deque[f] == i-k) f++;
      if(i>=k) sum+=a[Deque[f]];
  }

  g<<sum;

  return 0;

}