import sys
# input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
mod = 998244353

def fact(x):
    res = 1
    for i in range(1, x + 1):
        res *= i
        res %= mod
    return res

k = ni()
l, m = zip(*[na() for i in range(k)])
ans = 1
N = 0
res = 1
for i in range(k):
    N += l[i] * m[i]
    Z = fact(m[i]) * pow(fact(l[i]), m[i], mod) % mod
    res *= Z
    res %= mod

ans *= pow(res, mod-2, mod)
ans %= mod
ans *= fact(N)
ans %= mod

print(ans)