#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque <int> q;
int n,k,a[5000001],s;
int main()
{ in>>n>>k;
  for(int i=1;i<=n;i++)
    in>>a[i];
  for(int i=1;i<k;i++)
  { while(!q.empty() && a[q.back()]>a[i])
          q.pop_back();
    q.push_back(i);
  }
  for(int i=k;i<=n;i++)
  { if(i-q.front()==k)
       q.pop_front();
    while(!q.empty() && a[q.back()]>a[i])
          q.pop_back();
    q.push_back(i);
    s+=a[q.front()];
  }
  out<<s;
  in.close();
  out.close();
  return 0;
}