#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

int n,k,i;
long long A[600013],sol(0);
deque <int> Deque;
int main()
{
  cin>>n>>k; 
  for (i=1;i<=n;++i){
                     cin>>A[i];
                     while (!Deque.empty() && A[i] <= A[Deque.back()]) Deque.pop_back();     
                     Deque.push_back(i);
                     if (Deque.front()==i-k && !Deque.empty()) Deque.pop_front();
                     if (i>=k) sol+=A[Deque.front()];   
                    }
 cout<<sol;
 return 0;
}