MissingInteger

def solution(a)
  # write your code in Ruby 2.2
  i = 1
  hash = {}
  
  a.each do |element|
    hash[element] = 1
  end
  
  while 1 do  
    if hash[i].nil?
      return i
      break
    end  
      
    i += 1
  end
end