#include <fstream>

using namespace std;
int n,k,i,a[5000001],d[5000001],be,en;
long long sum;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    fin>>n>>k;
    be=1;
    for (i=1;i<=n;i++)
    {
      fin>>a[i];
      while (en>=be && a[i]<=a[d[en]])
      {
          en--;
      }
      en++;
      d[en]=i;
      while (be<=en && d[be]<i-k+1)
        be++;
        if (be<=en && i>=k)
        sum+=a[d[be]];
    }
    fout<<sum;
    fout.close();
    fin.close();

    return 0;
}