#include <fstream>
#include <deque>

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

std::deque <int> d;

int v[500001],n,k;

long long suma;

int main()
{
        int i;
        f>>n>>k;
        for(i=1;i<=n;i++)
          {
              f>>v[i];
              while(d.size() && v[i]<=v[d.back()])
              d.pop_back();
              d.push_back(i);
              if(d.front()==i-k) d.pop_front();
              if(i>=k) suma+=v[d.front()];

          }
          g<<suma;
        return 0;
}