# 4646 爬树的甲壳虫
# 数论的困难题 QAQ
# 重要的是公式的推导
n = int(input())
N = n
res = 0
p = 998244353

def qmi(a, b):
    res = 1
    while(b):
        if b & 1:
            res = res * a % p
        a = a * a % p
        b >>= 1
    return res


while(N):
    a, b = map(int, input().split())
    res = (1 + res) * b % p * qmi((b - a), p - 2) % p
    N -= 1
print(res)