inputs = input()
nums = inputs.split()
A = int(nums[0])
B = int(nums[1])
C = int(nums[3])
K = int(nums[2])

if C == A and C == B:
    print(K)
elif C == A or C == B:
    print(((2**(K-1))*K)%1000000007)
else:
    print(0)