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:
    x = K
    for i in range (K-1):
        x = x*2
        if x > 1000000007:
            x = x % 1000000007
    print(x)
else:
    print(0)