import sys
input = sys.stdin.readline

N=int(input())
mod=998244353

A=[tuple(map(int,input().split())) for i in range(N)]

SUM=0

for t,v in A:
    SUM+=t

NOW=1
ANS=0

def calc(k):
    return -(k*(k+1)//2)**2+k*(k+1)*(2*k+1)//6*SUM+k*(k+1)//2*(SUM+1)


for t,v in A:
    f=NOW
    l=NOW+t-1

    NOW+=t

    ANS+=v*(calc(l)-calc(f-1))

print(ANS//2%mod)