n=int(input())
nod=[]
mod=998244353
sumt=0
for _ in range(n):
    t,v=map(int,input().split())
    sumt+=t
    sumt%=mod
    nod.append((t,v))
s=1
ans=0
rev2=pow(2,mod-2,mod)
def f1(x):
    return (x*(x+1)//2)%mod
def f2(x):
    return (x*(x+1)*(2*x+1)//6)%mod
def f3(x):
    return (f1(x)**2)%mod
n=sumt%mod
for t,v in nod:
    g=s+t-1
    subans=0
    subans+=n*(f2(g)-f2(s-1))
    subans+=-(f3(g)-f3(s-1))
    subans+=(n+1)*(f1(g)-f1(s-1))
    subans*=v*rev2
    ans+=subans
    ans%=mod
    s+=t


print(ans%mod)