mod = 998244353
N = 10 ** 8 + 2
F = [1] * N
E = [1] * N
for i in range(2, N):
    F[i] = F[i-1]*i%mod
E[-1] = pow(F[-1], -1, mod)
for i in range(N-1, 0, -1):
    E[i-1] = E[i]*i%mod

def comb(a, b): #組合せ
    if b < 0:
        return 0
    if a < b:
        return 0
    return F[a] * E[b] * E[a-b] % mod

ans = 1
k = int(input())
cnt = 0
for _ in range(k):
    l, m = map(int, input().split())
    tmp = 1
    for i in range(m):
        tmp = comb(l*(i+1)-1, l-1) * tmp % mod
    ans = ans * tmp * comb(l * m + cnt, cnt) % mod
    cnt += l*m

print(ans)