i = 123456.to_i

s = 0
l = 1
i.size.times do
	s = s*10 + i%(i/10)
	i = i/10
	p "ROUND #{l}"
	p "s = #{s}; i = #{i}"
	l += 1
end

-----------

"ROUND 1"
"s = 6; i = 12345"
"ROUND 2"
"s = 65; i = 1234"
"ROUND 3"
"s = 654; i = 123"
"ROUND 4"
"s = 6543; i = 12"
"ROUND 5"
"s = 65430; i = 1"
int.rb:16:in `%': divided by 0 (ZeroDivisionError)
	from int.rb:16
	from int.rb:15:in `times'
	from int.rb:15