def fact(n):
    ret = n
    for i in range(n - 1, 1, -1):
        ret *= i
    return ret

def perms(a, b, k_fact):
    a_fact = fact(a)
    b_fact = fact(b)

    return k_fact // (a_fact * b_fact)

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

if c != a and c != b:
    print("0")
else:
    if a == b and b == c:
        print(k)
    else:
        if b == c:
            a = b

        s = 0
        k_fact = fact(k)
        for i in range(1, k):
            s += perms(i, k - i, k_fact) * i
            #print("s: " + str(s))

        s += k
        print(s % 1000000007)