#include<fstream>
using namespace std;
long long s,k,n,i,j,vminn,a[5000002];
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
       f>>n>>k;
       for(i=1;i<=n;i++)
       {
           f>>a[i];
       }
       s=0;
       for(i=1;i+k-1<=n;i++)
        {
            vminn=a[i];
            for(j=i+1;j<=i+k-1;j++)
              {
                  if(a[j]<vminn)
                   {
                       vminn=a[j];
                   }
              }
        s=s+vminn;
        }
       g<<s;
       g.close();
       f.close();
       return 0;

}