from math import factorial

# def speci_fact(cislo, do):
#     sum = 1
#     for i in range(cislo, do, -1):
#         sum  = sum * i
#     return sum
#
#
# def comb(hore, dole):
#     return speci_fact(hore,dole) / factorial(hore - dole)

def pascal(n):
    n -= 1
    line = [1]
    for k in range(max(n,0)):
        line.append(line[k]*(n-k)//(k+1))
    return line


inp = input()
a , b , k , c = [int(x) for x in inp.split()]



flag = 0
if (c != a) and (c != b):
    print(0)
    flag = 1
    exit(0)

if a == b:
    print(k)
    flag = 1
    exit(0)


if flag == 0:
    nasobic = k
    sum = 0
    modulko = 1000000007

#    for i in range(1,k):
#        sum += comb(k, i) * i
    ll = pascal(k+1)
    for i,pascal in enumerate(ll[1:]):
        sum += (i+1) * pascal

    sum  = sum % modulko
    print(sum)
    exit(0)