#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using mint = atcoder::modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<pair<int,int>> a(n);
    vector<int> ca(2 * n);
    for(int i = 0; i < n; i++){
        auto &&[l, r] = a[i];
        cin >> l >> r;
        l--;
        ca[2 * i] = l;
        ca[2 * i + 1] = r;
    }
    sort(ca.begin(), ca.end());
    ca.erase(unique(ca.begin(), ca.end()), ca.end());
    const int m = ca.size();
    vector<mint> imos(m);
    for(int i = 0; i < n; i++){
        auto &&[l, r] = a[i];
        mint div = mint(1) / (r - l);
        l = lower_bound(ca.begin(), ca.end(), l) - ca.begin();
        r = lower_bound(ca.begin(), ca.end(), r) - ca.begin();
        if (i == 0) continue;
        imos[r] += div;
        imos[l] -= div;
    }
    mint ans, sv = 1, div = 998244354 / 2;
    for(int i = m - 1; i >= a[0].first + 1; i--){
        imos[i - 1] += imos[i];
        mint len = ca[i] - ca[i - 1];
        if(i <= a[0].second) ans += len * (sv + imos[i] * (len - 1) * div);
        sv += imos[i] * len;
    }
    ans /= ca[a[0].second] - ca[a[0].first];
    cout << ans.val() << '\n';
}