N = int(input())
mod = 998244353
ans = 1
L,R = map(int,input().split())
D = R - L + 1
for i in range(1,N):
  l,r = map(int,input().split())
  if R < l:
    ans += 1
    continue
  elif r < L:
    continue
  ll = max(l,L)
  rr = min(r,R)
  d = r - l + 1
  n = rr - ll + 1
  res = (2 * r - ll - rr) * n
  res //= 2
  res = res * pow(d,-1,mod) % mod
  res += (ll - L)
  res = res * pow(D,-1,mod) % mod
  ans = (ans + res) % mod
print(ans)