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

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
   int N, K;
   int X[5000002];
   fin >> N >> K;
   for (int i = 1; i <= N; i++)
      fin >> X[i];

   deque<int> d;
   long long s = 0;

   for (int i = 1; i <= N; i++)
   {
      while (!d.empty() && X[d.back()] >= X[i])
      {
         d.pop_back();
      }
      d.push_back(i);
      if (d.front() == i - K)
      {
         d.pop_front();
      }
      if (i >= K)
      {
         s += X[d.front()];
      }
   }

   fout << s << endl;
   return 0;
}