import sys
input=sys.stdin.readline

N=int(input())

T=[0]*N
V=[0]*N
Mod=998244353
for i in range(N):
    T[i],V[i]=map(int,input().split())

P=[0]*N
Q=[0]*N

P[0]=1
Q[0]=T[0]

for i in range(1,N):
    P[i]=Q[i-1]+1
    Q[i]=P[i]+T[i]-1

    P[i]%=Mod
    Q[i]%=Mod

M=sum(T)%Mod

twenty_four_inv=pow(24,Mod-2,Mod)

def S(b):
    x=b

    x*=b+1
    x%=Mod

    x*=b+2
    x%=Mod

    x*=4*M+3-3*b
    return x%Mod

X=0
for v,p,q in zip(V,P,Q):
    X+=v*(S(q)-S(p-1))
    X%=Mod

print((twenty_four_inv*X)%Mod)