MOD = 998244353
INV2 = pow(2, MOD - 2, MOD)
N = int(input())
B, C = [], []
for _ in range(N):
    b, c = map(int, input().split())
    B.append(b)
    C.append(c)

dic = dict()
dic2 = dict()
for i in range(N):
    p = pow(C[i] - B[i] + 1, MOD - 2, MOD)
    if B[i] not in dic:
        dic[B[i]] = 0
    if B[i] not in dic2:
        dic2[B[i]] = 0
    dic[B[i]] += p
    dic[B[i]] %= MOD
    dic2[B[i]] += p * p
    dic2[B[i]] %= MOD
    if C[i] + 1 not in dic:
        dic[C[i] + 1] = 0
    if C[i] + 1 not in dic2:
        dic2[C[i] + 1] = 0
    dic[C[i] + 1] -= p
    dic[C[i] + 1] %= MOD
    dic2[C[i] + 1] -= p * p
    dic2[C[i] + 1] %= MOD


s, s2 = 0, 0
ls = list(dic.keys())
ls.sort()
prev = ls[0]
ans = 0

for i in range(len(ls)):
    ans += (s * s - s2) * INV2 * (ls[i] - prev)
    ans %= MOD

    prev = ls[i]
    s += dic[ls[i]]
    s %= MOD
    s2 += dic2[ls[i]]
    s2 %= MOD


fac = 1
for i in range(1, N + 1):
    fac *= i
    fac %= MOD

fans = ((N * (N - 1) * INV2 - ans) * INV2 * fac) % MOD
print(fans)