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

using S = pair<mint, mint>;
using F = mint;
S op(S lhs, S rhs){
    return make_pair(lhs.first + rhs.first, lhs.second + rhs.second);
}
S e(){
    return make_pair(0, 0);
}
S mapping(F f, S x){
    return make_pair(x.first + f * x.second, x.second);
}
F composition(F f, F g){
    return f + g;
}
F id(){return 0;}


int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<pair<int,int>> a(n), b(n);
    vector<int> ca(2 * n);
    for(int i = 0; i < n; i++){
        int l, r;
        cin >> l >> r;
        a[i] = make_pair(l, r);
        ca[2 * i] = l;
        ca[2 * i + 1] = r + 1;
    }
    sort(ca.begin(), ca.end());
    ca.erase(unique(ca.begin(), ca.end()), ca.end());
    vector<S> tmp(ca.size());
    for(int i = 0; i + 1 < ca.size(); i++){
        tmp[i].second = ca[i + 1] - ca[i];
    }
    lazy_segtree<S, op, e, F, mapping, composition, id> seg(tmp);
    mint ans;
    for(int i = 0; i < n; i++){
        int l, r;
        tie(l, r) = a[i];
        mint div = mint(1) / (r - l + 1);
        l = lower_bound(ca.begin(), ca.end(), l) - ca.begin();
        r = upper_bound(ca.begin(), ca.end(), r) - ca.begin();
        ans += seg.prod(l, r).first * div;
        seg.apply(l, r, div);
    }
    seg = lazy_segtree<S, op, e, F, mapping, composition, id>(tmp);
    for(int i = n - 1; i >= 0; i--){
        int l, r;
        tie(l, r) = a[i];
        mint div = mint(1) / (r - l + 1);
        l = lower_bound(ca.begin(), ca.end(), l) - ca.begin();
        r = upper_bound(ca.begin(), ca.end(), r) - ca.begin();
        ans += seg.prod(l, r).first * div;
        seg.apply(l, r, div);
    }
    ans = mint(n) * (n - 1) - ans;
    ans /= 2;
    for(int i = 3; i <= n; i++) ans *= i;
    cout << ans.val() << '\n';
}