import sys
input = lambda :sys.stdin.readline()[:-1] 

from math import sqrt, pi, exp, log, log10, sin, cos, tan, ceil, floor, perm, comb, gcd, modf, prod, inf, nan

def main():
    X, Y, Z, W = map(int, input().split())

    if Z == 0: # 最後はXから1人
        a = X   # X人からX-1人を選ぶ
        b = comb(Y, W) % 998244353   # Y人からY-W人を選ぶ
        n = X + Y - W - 1   # X-1, Y-W 人を合わせた順列
    
        ans = a * b % 998244353 

    elif W == 0:
        a = comb(X, Z) % 998244353
        b = Y
        n = X + Y - Z - 1   # X-Z, Y-1 人を合わせた順列

        # print(a,b,n)

        ans = a * b % 998244353 

    for i in range(n, 0, -1):
        ans = ans * i % 998244353

    print(ans)
    
if __name__ == '__main__':
    main()