#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();
}