# https://yukicoder.me/problems/no/3003

import math

MOD = 998244353



def main():
    K = int(input())
    lm = []
    for _ in range(K):
        L, M = map(int, input().split())
        lm.append((L, M))

    n = 0
    for l, m in lm:
        n += l * m    

    def calc_factorial(n):
        ans = 1
        for x in range(1, n + 1):
            ans *= x
            ans %= MOD
        return ans

    answer = calc_factorial(n)
    for l, m in lm:
        x0 = calc_factorial(l)
        inv_x0 = pow(x0, MOD - 2, MOD)
        x = pow(inv_x0, m, MOD)
        answer *= x
        answer %= MOD
        x0 = calc_factorial(m)
        inv_x0 = pow(x0, MOD - 2, MOD)
        answer *= inv_x0
        answer %= MOD
    print(answer)



    





if __name__ == "__main__":
    main()