[tetroel]

n = gets.chomp.to_i
puts (1..n).to_a.to_s.each_char.inject(0){|sum, d| sum += d.to_i}

I'm particularly interested in the second string of the code.

[Skaggles]

Basically, it works by converting a range of integers into an array, then a string. Then, using inject, it goes through and reduces the string by summing up all the integers two at a time. The Ruby documentation could definitely give you some better in-depth information about what exactly is happening. This code can be simplified and looks like it was purposely made to be over-complicated.