N = gets.to_i

def build_str(ch, len, is_first = false)
  if is_first
    res = ch * len
    ch.succ!
  else
    res = ch * len
    ch.succ!
    res << ch
    ch.succ!
  end

  res
end

cur = 'a'
is_first = true
len = 0
ans = ''

30.times do |i|
  if N[i] == 0
    if is_first
      str = build_str(cur, i, true)
      is_first = false
      ans << str
    end
  else
    if is_first
      len += 1
    else
      str = build_str(cur, i)
      ans << str
    end
  end
end

if ans[-1] <= 'z'
  puts ans
else
  puts 'sushi'
end