MOD = 998244353

K = int(input())
N = 0
Y = []
for _ in range(K):
    l, m = map(int, input().split())
    Y.append((l, m))
    N += l * m

factorial = [1]
for i in range(1, N + 1):
    factorial.append(factorial[-1] * i % MOD)

ans = factorial[N]
for l, m in Y:
    ans = ans * pow(factorial[l],-m,MOD) * pow(factorial[m],-1,MOD) % MOD

print(ans)