import sys
input = sys.stdin.readline

from operator import itemgetter

mod=998244353

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]
    
    if com==1:
        now1+=pow(length,-1,mod)
    else:
        now1-=pow(length,-1,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+=now1*now1*(z-x)%mod
        #print("!",now1)
        ANS1%=mod

for b,c in LIST:
    k=c-b+1

    ANS1-=pow(k,-1,mod)
    ANS1%=mod

#print(ANS1)



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

#print(ANS2)


F=[1]
for i in range(1,1000000):
    F.append(F[-1]*i%mod)


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