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)