#include <atcoder/all>
#include <bits/stdc++.h>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace atcoder;
using namespace std;

typedef long long ll;

using mint = modint998244353;

mint f(ll l1, ll r1, ll l2, ll r2) {
    // if (r2 <= l1)
    //     return 0;
    // if (r1 < l2)
    //     return 1;
    mint p = 0;

    vector<pair<ll, ll>> v;

    auto f = [&](ll xi) {
        ll ret = max(0LL, r2 - max(l2 - 1, xi));
        v.emplace_back(xi, ret);
        return;
    };
    f(l1);
    f(l1 + 1);
    f(r1);
    f(r1 + 1);
    f(l2);
    f(l2 + 1);
    f(r2);
    f(r2 + 1);
    sort(v.begin(), v.end());
    rep(i, 0, v.size() - 1) {
        ll x1 = v[i].first, y1 = v[i].second;
        ll x2 = v[i + 1].first, y2 = v[i + 1].second;
        if (x1 < l1)
            continue;
        if (x1 > r1)
            break;
        if (y1 == y2) {
            p += mint(y1) * (x2 - x1);
        } else if (y1 > y2) {
            p += (mint)(y1 + y2 + 1) * (x2 - x1) / 2;
        } else if (y1 < y2) {
            p += (mint)(y1 + y2 - 1) * (x2 - x1) / 2;
        }
    }
    p /= (r1 - l1 + 1) * (r2 - l2 + 1);
    return p;
}

void out(mint n) {
    rep(i, 0, 100) rep(j, 1, 100) {
        mint nw = (mint)i / j;
        if (nw == n) {
            cout << i << "/" << j << endl;
            return;
        }
    }
}

int main() {
    int n;
    cin >> n;
    vector<int> l(n), r(n);
    rep(i, 0, n) { cin >> l[i] >> r[i]; }
    mint ans = 1;
    rep(i, 1, n) { ans += f(l[0], r[0], l[i], r[i]); }
    cout << ans.val() << endl;
    // out(ans);
}