import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
mod = 998244353

n = ni()
l, r = zip(*[na() for i in range(n)])
l = list(l)
r = list(r)
for i in range(n):
    l[i], r[i] = -r[i], -l[i]

L, R = l[0]-1, r[0]-1
ans = 0
for i in range(1, n):
    res = 0
    D, U = max(L, l[i]), min(R, r[i])
    # (U - l[i] + 1) + (U-l[i]) + (U-l[i]-1) + ... + (D - l[i] + 1)
    if D <= U:
        res += (U + D - 2 * l[i] + 2) * (U - D + 1) // 2
    F = max(U, L - 1)
    if F < R: #
        res += (R - F) * (r[i] - l[i] + 1)
    
    ans += res * pow(R - L + 1, mod -2, mod) % mod * pow(r[i] - l[i] + 1, mod - 2, mod) % mod
    ans %= mod
    #print(res, res * pow(R - L + 1, mod -2, mod) % mod * pow(r[i] - l[i] + 1, mod - 2, mod) % mod)

print((1 + ans) % mod)