#!ruby
n,k,*a=gets(p).split.map(&:to_i)
i=0
d=n/k
r=[0,a[k-1]]

m = a[k-1]
2.upto(d) do |c|
  r=[0,a[k-1]]
  k.upto(a.size-1) do |i|
    c.downto(2) do |b|
      next if i<k*b-1 || r[b-1].nil?
      v = r[b-1]+a[i]
      if r[b].nil? || r[b] > v then
        r[b] = v
      end
    end
    r[1] = [r[1],a[i]].min if i<=(k-1)*c
  end
  m = [m,r[c]].min if r[c]
end      
p m