K=int(input())
p=998244353
ma = 10**8 + 1
ans=[1 for _ in range(ma)]
for i in range(2,ma):
    ans[i]=ans[i-1]*i%p
fa=1
s=0
for i in range(K):
    l,m=map(int,input().split())
    s+=l*m
    fa*=pow(pow(ans[l],-1,p)%p,m,p)
    fa*=pow(ans[m],-1,p)
    fa%=p
#print(ans)
fa*=ans[s]
fa%=p
print(fa)