function reverse_digits(n::Integer)
    pot = floor(Int, log10(n))
    d = 0
    for i = pot:-1:0
        dig = div(n, 10^i)
        if dig == 0
            continue
        end
        d += dig * 10^(pot-i)
        n = rem(n, (dig * 10^i))
    end
    d
end