MOD = 998244353
K = int(input())
X = [list(map(int,input().split())) for _ in range(K)]
L = [X[i][0] for i in range(K)]
M = [X[i][1] for i in range(K)]
N = 0
for i in range(K):
    N += L[i]*M[i]
C = {}
for i in range(K):
    if M[i] not in C:
        C[M[i]] = 0
    C[M[i]] += 1
C = sorted(list(C.items()),key=lambda x:x[0])
ans = 1
a = 1
j1 = 0
j2 = 0
for i in range(1,N+1):
    ans = (ans*i)%MOD
    a = (a*i)%MOD
    if j1<K and i==L[j1]:
        b = pow(a,M[j1],MOD)
        ans = (ans*pow(b,MOD-2,MOD))%MOD
        j1 += 1
    if j2<len(C) and i==C[j2][0]:
        b = pow(a,C[j2][1],MOD)
        ans = (ans*pow(b,MOD-2,MOD))%MOD
        j2 += 1
print(ans)