MOD = 998244353i64

def inv(v : Int64)
  pow(v, MOD - 2)
end

def pow(v : Int64, p)
  ret = 1i64
  while p > 0
    if (p & 1i64) != 0
      ret *= v
      ret %= MOD
    end
    v *= v
    v %= MOD
    p >>= 1
  end
  ret
end

n = read_line.to_i
l0, r0 = read_line.split.map(&.to_i64)
ans = 1i64
(n - 1).times do
  l1, r1 = read_line.split.map(&.to_i64)
  next if r1 <= l0
  if r0 < l1
    ans += 1
    next
  end
  add = 0i64
  if l0 < l1
    add += (l1 - l0) * (r1 - l1 + 1)
  end
  lo = {l0, l1}.max
  hi = {r0, r1}.min
  add += ((r1 - lo) + (r1 - hi)) * (hi - lo + 1) // 2
  add *= inv(r0 - l0 + 1)
  add %= MOD
  add *= inv(r1 - l1 + 1)
  add %= MOD
  ans += add
end
puts ans % MOD