#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++) {
        if (r[0] < l[i]) {
            ans++;
            continue;
        } else if (r[i] < l[0]) {
            continue;
        }
        // 絶対に負け
        int lose_cnt = max(0, l[i] - r[0]);
        mint tmp = lose_cnt * mint(r[i] - l[i] + 1);
        int lb = max(l[0], l[i]), rb = min(r[0], r[i]);
        tmp += mint(2 * r[i] - lb - rb) * mint(rb - lb + 1) / 2;
        tmp /= mint(r[i] - l[i] + 1) * mint(r[0] - l[0] + 1);
        ans += tmp;
    }
    cout << ans.val() << endl;
}