Integer to Roman

Seven symbols represent Roman numerals:

Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

Rules:

• Append the symbol of the maximal value that can be subtracted from the input.
• Use subtractive forms for 4 and 9: IV, IX, XL, XC, CD, CM.
• Powers of 10 (I, X, C, M) can appear at most 3 times consecutively.

Given an integer num, convert it to a Roman numeral.

Example 1:

Input:  num = 3749
Output: "MMMDCCXLIX"

Example 2:

Input:  num = 58
Output: "LVIII"

Example 3:

Input:  num = 1994
Output: "MCMXCIV"

Constraints:

• 1 <= num <= 3999