#!/usr/bin/env lua

--[[
Challenge 120

TASK #1 - Swap Odd/Even bits
Submitted by: Mohammad S Anwar
You are given a positive integer $N less than or equal to 255.

Write a script to swap the odd positioned bit with even positioned bit and
print the decimal equivalent of the new binary representation.

Example
Input: $N = 101
Output: 154

Binary representation of the given number is 01 10 01 01.
The new binary representation after the odd/even swap is 10 01 10 10.
The decimal equivalent of 10011010 is 154.

Input: $N = 18
Output: 33

Binary representation of the given number is 00 01 00 10.
The new binary representation after the odd/even swap is 00 10 00 01.
The decimal equivalent of 100001 is 33.
--]]

function swap_bits(n)
    local result = 0
    local bits = 1
    while n > 0 do
        if n % 2 ~= 0 then result = result + 2*bits end
        n = math.floor(n / 2)
        if n % 2 ~= 0 then result = result + 1*bits end
        n = math.floor(n / 2)
        bits = bits*4
    end
    return result
end

n = tonumber(arg[1])
n = swap_bits(n)
io.write(n, "\n")