mod = 998244353
n = 10**8+5
fact = [1] * (n + 1)
invfact = [1] * (n + 1)
for i in range(1, n):
    fact[i + 1] = ((i+1) * fact[i]) % mod
invfact[n] = pow(fact[n], mod - 2, mod)
for i in range(n - 1, -1, -1):
    invfact[i] = invfact[i + 1] * (i + 1) % mod

def comb(n, r):
    if n < 0 or r < 0 or n - r < 0:
        return 0
    return fact[n] * invfact[r] * invfact[n - r] % mod

K = int(input())
L, M = [0] * K, [0] * K
S = 0
for i in range(K):
    L[i], M[i] = map(int, input().split())
    S += L[i] * M[i]
    
ans = 1
for i in range(K):
    ans *= comb(S, L[i] * M[i])
    S -= L[i] * M[i]
    ans *= fact[L[i] * M[i]]
    ans *= pow(invfact[L[i]], M[i], mod)
    ans *= invfact[M[i]]
    ans %= mod
    
print(ans)