import sys
input = sys.stdin.readline

mod = 998244353
N = int(input())
events = []
for _ in range(N):
    B, C = map(int, input().split())
    C += 1
    l = pow(C-B, mod-2, mod)
    events.append((B, l, 0))
    events.append((C, l, 1))
events.sort(key=lambda p: p[0])
i = 0

slen = 0
slen2 = 0

prv = 0
ans = 0
inv2 = pow(2, mod-2, mod)

while i < len(events):
    x = events[i][0]
    ans = (ans + (x - prv) * (slen**2-slen2) % mod * inv2) % mod
    while i < len(events) and events[i][0] == x:
        x, l, t = events[i]
        if t == 0:
            slen += l
            slen2 += l**2
        else:
            slen -= l
            slen2 -= l**2
        slen %= mod
        slen2 %= mod
        i += 1
    prv = x

ans = (N*(N-1)//2-ans) % mod
fact = 1
for i in range(1, N+1):
    fact = fact*i % mod
ans = ans*fact*inv2 % mod

print(ans)