Write a program called `rn`. The objective is to convert a number, given as an argument, into a roman number and print it with its roman number calculation.
The program should have a limit of `4000`. In case of an invalid number, for example `"hello"` or `0` the program should print `ERROR: can not convert to roman digit`.
For example, the number 1732 would be denoted MDCCXXXII in Roman numerals. However, Roman numerals are not a purely additive number system. In particular, instead of using four symbols to represent a 4, 40, 9, 90, etc. (i.e., IIII, XXXX, VIIII, LXXXX, etc.), such numbers are instead denoted by preceding the symbol for 5, 50, 10, 100, etc., with a symbol indicating subtraction. For example, 4 is denoted IV, 9 as IX, 40 as XL, etc.
