#include <fstream>
#include <deque>
using namespace std;

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

deque<int>deck;
int vec[500005],i,n,k;
long long minim;

int main()
{f>>n>>k;
 for (i=1;i<=n;i++)
 {f>>vec[i];
  while (!deck.empty() && vec[deck.back()]>vec[i])
     deck.pop_back();
  deck.push_back(i);
  if(deck.front()<=i-k)
        deck.pop_front();
  if (i>=k)
    minim+=vec[deck.front()];
 }
 g<<minim;
 f.close();
 g.close();
 return 0;
}