#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,i,j,ii,minim,a[5000001];
long long sum;
int main()
{
 f>>n;
 f>>k;
 minim=10000001;
 for(i=1;i<=k;i++)
 {
    f>>a[i];
    if(a[i]<minim)
    {
        minim=a[i];
        ii=i;
    }
 }
 for(j=k+1;j<=n;j++)
 {
    f>>a[j];
 }
 sum=minim;
 for(j=k+1;j<=n;j++)
 {
     if(a[j]<minim)
     {
         minim=a[j];
         ii=j;
         sum=sum+minim;
     }
     else if(j-k+1<=ii)
     {
         sum=sum+minim;
     }
     else
     {
         minim=10000001;
         for(i=j-k+1;i<=j;i++)
         {
             if(a[i]<minim)
            {
                minim=a[i];
                ii=i;
            }
         }
         sum=sum+minim;
     }
 }
 g<<sum;
 return 0;
}