from collections import Counter

K=int(input())
LM=[list(map(int,input().split())) for i in range(K)]

mod=998244353

K=[]

for l,m in LM:
    K.append(l*m)

ANS=1
SUM=sum(K)

PLUS=Counter()
INV=Counter()

PLUS[SUM]+=1
for i in range(len(K)):
    if SUM-K[i]>0:
        INV[K[i]]+=1
    else:
        INV[SUM]+=1
    SUM-=K[i]
        

for l,m in LM:
    SUM=l*m
    PLUS[SUM]+=1
    INV[l]+=m

    INV[m]+=1

f=1
ANS=1
for i in range(1,sum(K)+1):
    f=f*i%mod
    if i in PLUS:
        ANS=ANS*pow(f,PLUS[i],mod)%mod
    if i in INV:
        ANS=ANS*pow(pow(f,INV[i],mod),mod-2,mod)%mod

print(ANS%mod)