#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  int L, R;
  cin >> L >> R;
  L--;
  mint ans = 1;
  rep(_, n - 1) {
    int l, r;
    cin >> l >> r;
    l--;
    ll c1 = max(0, min(R, l) - L), c2 = max(0, min(R, r) - max(L, l)), c3 = max(0, r - max(R, l));
    ll cnt = c2 * (c1 + c3) + c1 * c3 + c2 * (c2 - 1) / 2;
    ans += cnt / (mint(r - l) * (R - L));
  }
  cout << ans.val() << '\n';
}