import sys
import io, os
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

from operator import itemgetter

mod=998244353

F=[1]
for i in range(1,200020):
    F.append(F[-1]*i%mod)

# 高速ベキ乗
def fast_pow(x,y):
    ANS=1
    while y>0:
        if y%2==1:
            ANS=ANS*x%mod
            y-=1

        if y>0:
            x=x*x%mod
            y//=2
    return ANS

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

Q=[]

for b,c in LIST:
    Q.append((b,c-b+1,1))
    Q.append((c+1,c-b+1,2))

Q.sort(key=itemgetter(1))
Q.sort(key=itemgetter(0))

now1=0
ANS1=0

for i in range(len(Q)):
    x,length,com=Q[i]

    LINV=fast_pow(length,mod-2)
    
    if com==1:
        now1=(now1+LINV)%mod
        ANS1=(ANS1-LINV)%mod
    else:
        now1=(now1-LINV)%mod

    if i+1<len(Q) and x!=Q[i+1][0]:
        z=Q[i+1][0]

        # [x,z)の間を考え、答えに加算。

        ANS1=(ANS1+now1*now1%mod*(z-x)%mod)%mod


ANS2=(N*(N-1)//2-ANS1*fast_pow(2,mod-2))%mod

print(ANS2*F[N]*fast_pow(2,mod-2)%mod)