def str2num(str)
    num = 0
    for i in str.split('')
        num *= 10
        for j in '0123456789'.split('')
            if i > j
                num += 1
            else
                break
            end
        end
    end
    return num
end

rs = str2num('2019')
puts rs # 2019
puts rs.instance_of? Integer # true