The greatest common divisor of 2 numbers, also known as the highest common factor, is the highest whole number that can divide those 2 numbers without leaving any remainder.
The formula for GCD is as below: [Do note that a > b for all cases]
2 numbers, a and b. It is not guarenteed that a is always greater than b or vice versa. However, both numbers will be below 109
Output a single integer, the greatest common divisor of the 2 numbers.