import sys 
N = input().split()
A = int(N[0])
B = int(N[1])
K = int(N[2])
C = int(N[3])
if K == 0:
	print(0)
	sys.exit()
if C != A and C != B:
	print(0)
	sys.exit()
if A == B:
	print(2**(K-1)*K*2)
else:
	print(2**(K-1)*K)