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

using mint = modint998244353;

int main() {
    int N;
    cin >> N;

    vector<pair<int, int>> interval(N);
    for (int i = 0; i < N; i++) cin >> interval[i].first >> interval[i].second;

    mint ans = 1;
    for (int i = 1; i < N; i++) {
        auto [li, ri] = interval[i];
        auto [l0, r0] = interval[0];
        int l = max(li, l0);
        int r = min(ri, r0);

        mint t = min(l-l0, r0-l0+1);
        if (l <= r) t += (mint(2)*ri-l-r)*(r-l+1)/(ri-li+1)/2;
        t /= r0-l0+1;
        
        ans += t;
    }

    cout << ans.val() << endl;
}