def solve s, k
  h = Hash.new(0)
  s.chars.sort[0...k].each { |e| h[e.to_sym] += 1 }
  s = s.chars
  o = []
  s.each do |v|
    if h[v.to_sym] > 0
      h[v.to_sym] -= 1
    else
      o << v
    end
  end
  o.join
end