#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,inceput,sfarsit,q[5000001],mi,i,x,j;
long long s;
int main()
{
   f>>n>>k;
   inceput=1;
   for(i=1;i<=n;i++)
   {
       f>>x;
       q[++sfarsit]=x;
       if(sfarsit-inceput==k-1)
       {
           mi=1000001;
           for(j=inceput;j<=sfarsit;j++)
           {

               if(mi>q[j])
                mi=q[j];
           }

           s+=mi;
           inceput++;
       }
   }
   g<<s;
    return 0;
}