What will be the output of this code?

What will be the output of this code?

class X:
    def who(self):
        print('X')

class Y(X):
    def who(self):
        print('Y')

class Z(X):
    def who(self):
        print('Z')

class W(Y, Z):
    def who(self):
        super().who()

w = W()
w.who()