#include <fstream>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5100000],n,i,p=1,k,u,d[5100000];
long long e;
int main()
{
    f>>n>>k;
    for (i=1;i<=n;i++)
      f>>a[i];
    for (i=1;i<=n;i++)
     {
         while (p<=u && a[i]<=a[d[u]])u--;
         d[++u]=i;
         if (d[p]==i-k)p++;
         if (i>=k)e+=a[d[p]];

     }
     g<<e;
    f.close();
    g.close();
}