#!/usr/bin/env lua

--[[
Challenge 119

TASK #2 - Sequence without 1-on-1
Submitted by: Cheok-Yin Fung
Write a script to generate sequence starting at 1. Consider the increasing
sequence of integers which contain only 1’s, 2’s and 3’s, and do not have any
doublets of 1’s like below. Please accept a positive integer $N and print the
$Nth term in the generated sequence.

1, 2, 3, 12, 13, 21, 22, 23, 31, 32, 33, 121, 122, 123, 131,

Example
Input: $N = 5
Output: 13

Input: $N = 10
Output: 32

Input: $N = 60
Output: 2223
--]]

function next_seq(n)
    while true do
        n = n+1
        if not string.match(n, "[04-9]") and
           not string.match(n, "11") then
            return n
        end
    end
end

num = tonumber(arg[1])
n = 0
for i = 1, num, 1 do
    n = next_seq(n)
end
io.write(n, "\n")