#def pow(n, k):
    #if k % 2 == 0:

A,B,K,C = [int(x) for x in input().split()]
if C == A or C == B:
    n = int(2**(K-1) * K)
    if A== B:
        print(K)
    else:
        print(n % 1000000007)
else:
    print(0)