GATE Computer Science (CS) 2021 Shift 2 Solved Paper

Consider the following ANSI C function:
int SomeFunction (int x, int y)
{
if ( (x == 1) I I (y == 1)) return 1;
if (x == y) return x;
if (x > y) return SomeFunction(x - y, y);
if (y > x) return SomeFunction(x, y - x);
}
The value returned by SomeFunction(15, 255) is _______.