Minimum squares to evenly cut a rectangle

Given a rectangular sheet of length l and width w. we need to divide this sheet into square sheets such that the number of square sheets should be as minimum as possible.
Examples:
 

Input :l= 4 w=6 
Output :6 
We can form squares with side of 1 unit, But the number of squares will be 24, this is not minimum. If we make square with side of 2, then we have 6 squares. and this is our required answer. 
And also we can't make square with side 3, if we select 3 as square side, then whole sheet can't be converted into squares of equal length. 
 

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Input :l=3 w=5 
Output :15

Optimal length of the side of a square is equal to GCD of two numbers
 

6

Time Complexity: O(log(min(a, b))), where a and b are two parameters of gcd.

Auxiliary Space: O(log(min(a, b)))