M=998244353
K=int(input())
N=0
a=1
f=1
l=0
q=[]
for _ in range(K):
  nl,m=map(int,input().split())
  while l<nl:
    l+=1
    f*=l
    f%=M
  a*=pow(pow(f,m,M),M-2,M)
  a%=M
  q+=[m]
  N+=l*m
for i in range(1,N+1):
  a*=i
  a%=M
q.sort()
f=1
l=0
for nl in q:
  while l<nl:
    l+=1
    f*=l
    f%=M
  a*=pow(f,M-2,M)
  a%=M
print(a)