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

# print(a.split(' '))

sum = 0
if c == a or c == b:
    sum = (2 ** (k-1)) * k % 1000000007

print(sum)