R=range
J=lambda:list(map(int,input().split()))
v=[]
N=0
for k in R(sum(J())):L,M=J();N+=L*M;v+=[[L,-M],[M,-1]]
v+=[[N,1]]
f=t=1
P=998244353
a=1
for b,e in sorted(v):
	while t<b:t+=1;f=f*t%P
	a=a*pow(f,e,P)%P
print(a)