import sys
a, b, k, c = [int(i) for i in input().split()]

if c!=a and c!=b:
  print(0)
  sys.exit(0)
if a==b:
  print(k)
  sys.exit(0)
if k==0:
  print(0)
  sys.exit(0)
print(2**k*k//2 % 1000000007)