M=998244353

def s1(n):
  return n*(n+1)*pow(2,M-2,M)%M

def s2(n):
  return n*(n+1)*(2*n+1)*pow(6,M-2,M)%M

def s3(n):
  return (n*(n+1)*pow(2,M-2,M))**2%M

n=int(input())
q=[tuple(map(int,input().split())) for i in range(n)]
L=sum(t for t,_ in q)%M
a=0
l=0
for t,v in q:
  a+=v*pow(2,M-2,M)*((s2(l+t)-s2(l))*L+(s1(l+t)-s1(l))*L-(s3(l+t)-s3(l))+(s1(l+t)-s1(l)))
  a%=M
  l+=t
  l%=M
print(a)