#include <bits/stdc++.h>
using namespace std;

void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

#include <atcoder/modint>
using mint = atcoder::modint998244353;
int main() {
    fast_io();
    int n;
    cin >> n;
    vector<int> l(n), r(n);
    for (int i = 0; i < n; i++) {
        cin >> l[i] >> r[i];
    }
    mint ans = 1;
    for (int i = 1; i < n; i++) {
        int lo_lose = l[0], hi_lose = min(r[0], l[i] - 1);
        int len = max(0, hi_lose - lo_lose + 1);
        mint cnt = mint(r[i] - l[i] + 1) * max(0, hi_lose - lo_lose + 1);
        // l[0] <= x <= r[0] かつ x <= r[i] となる区間
        int lo = max(l[0], l[i]), hi = min(r[0], r[i]);
        if (lo <= hi) {
            // sum_{j = lo}^{hi} r[i] - j
            cnt += mint(hi - lo + 1) * (2 * r[i] - lo - hi) / 2;
        }
        ans += cnt / mint(r[0] - l[0] + 1) / mint(r[i] - l[i] + 1);
    }
    cout << ans.val() << endl;
}