a,b,k,c = input().split() a = int(a) b = int(b) k = int(k) c = int(c) if k == 0: print(0) elif c != a and c != b: print(0) elif a == b: print(k) else: res = k comb = k for i in range(2, k+1): comb *= k-i+1 comb //= i - 1 res+= comb print(res % 1000000007)