A, B, K, C, = input().split()
A = int(A)
B = int(B)
K = int(K)
C = int(C)

if K == 0:
    print(0)
elif C != A and C != B:
    print(0)
else:

    if A == B:
        vysledek = K
    else:
        vysledek = ((2 ** (K - 1)) * K) % 1000000007

    print(vysledek)