# frozen_string_literal: true
in_n, in_k = gets.chomp.split.map(&:to_i)
in_a = gets.chomp.split.map(&:to_i)

dp = Array.new((in_n + 1) * (in_k + 1), -(10**100))
if in_k > in_n.ceildiv(2)
  puts "Impossible"
  exit
end

stride = in_k + 1
dp[0] = 0
dp[stride] = 0
dp[stride + 1] = in_a[0]
in_a.each_with_index do |a, i|
  next if i == 0
  prev2_base = (i-1) * stride
  prev_base = (i) * stride
  current_base = (i+1) * stride

  dp[current_base] = 0
  1.upto(in_k) do |k|
    dp[current_base + k] = [dp[prev_base + k], dp[prev2_base + k - 1] + a].max
  end
end

puts ((in_n).times.map { |n| dp[stride * (n+1) + in_k]}.max)