from typing import List
def barrels(a,b,k,c):
    if c in [a,b]:
        return int(((2**k) * k) / 2 % 1000000007)
 


a = input()
a = a.replace(" ", "")
print(barrels(int(a[0]),int(a[1]),int(a[2]),int(a[3])))