1st call SomeFunction(15, 255)
2nd call SomeFunction(15, 240)
3rd call SomeFunction(15, 225)
……...
Now for each call 15 is subtracted from 255 and 255 is a multiple of 15.
once the call reaches SomeFunction(15, 15) it’ll return x i.e 15.
So output is 15.
Note: This is a method to find GCD by repeated subtraction.