#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int d[5000001];
int v[5000001],n,k,p,u;
long long s;
int main()
{
   cin>>n>>k;
   for(int i=1;i<=n;i++)
    cin>>v[i];
  d[1]=1;
  p=1;
  u=1;
  for(int i=2;i<=n;i++)
  {
      while(p<=u&&v[d[u]]>v[i])
        u--;
      d[++u]=i;
      if(d[p]==i-k)
        p++;
      if(i>=k)
        s+=v[d[p]];
  }
   cout<<s;
    return 0;
}