N=int(input())
mod=998244353
this=0
su=0
ans=0
L=list()
for i in range(N):
  t,a=map(int,input().split())
  L.append([t,a])
  su+=t
for i in range(N):
  thisans=0
  t,a=L[i]
  this+=1
  this2=this+t-1
  n=this-1
  m=this2
  k=((m+2)*(m+1)*m//6)-((n+2)*(n+1)*n//6)
  thisans+=k*(su+1)*a
  f=(m*(m+1)*(m+2)*(3*m+1)//24)-(n*(n+1)*(n+2)*(3*n+1)//24)
  thisans-=f*a
  ans+=thisans
  ans%=mod
  this=this2
print(ans)