R=range
J=lambda:list(map(int,input().split()))
N=0
a=f=l=1
P=998244353
for k in R(sum(J())):
	L,M=J();N+=L*M;g=1
	while l<L:l+=1;f=f*l%P
	for j in R(2,M+1):g=g*j%P
	a=a*pow(f,-M,P)*pow(g,-1,P)%P
while l<N:l+=1;f=f*l%P
print(a*f%P)