a, b, k, c = input().split(" ")
a, b, k, c = int(a), int(b), int(k), int(c)

if c != a and c != b:
    print(0)
    exit(0)

res = 1
for i in range(0, k-1):
    res *= 2
    res %= 1000000007
res *= k
res %= 1000000007
if a == b:
    res = k

print(int(res))