#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
istream &operator>>(istream &is, modint &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint &a) { return os << a.val(); }
istream &operator>>(istream &is, modint998244353 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint998244353 &a) { return os << a.val(); }
istream &operator>>(istream &is, modint1000000007 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint1000000007 &a) { return os << a.val(); } 

typedef long long ll;
typedef vector<vector<int>> Graph;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define FOR(i,l,r) for (int i = l;i < (int)(r); i++)
#define rep(i,n) for (int i = 0;i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define my_sort(x) sort(x.begin(), x.end())
#define my_max(x) *max_element(all(x))
#define my_min(x) *min_element(all(x))
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const int INF = (1<<30) - 1;
const ll LINF = (1LL<<62) - 1;
const int MOD = 998244353;
const int MOD2 = 1e9+7;
const double PI = acos(-1);
vector<int> di = {1,0,-1,0};
vector<int> dj = {0,1,0,-1};

#ifdef LOCAL
#  include <debug_print.hpp>
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

using mint = modint998244353;
// using mint = double;

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    int N; cin >> N;
    vector<int> l(N), r(N);
    rep(i, N) {
        cin >> l[i] >> r[i];
        l[i]--;
    }

    mint inv2 = mint(1) / mint(2);

    mint ans = 1;
    FOR(i, 1, N){

        if(r[0] <= l[i]) ans += 1;
        else if(l[0] >= r[i]);
        else {
            auto func = [&](mint left, mint right){
                mint res = 0;
                res += (r[i] - 1) * (right - left);
                res -= right * (right - 1) * inv2;
                res += left * (left - 1) * inv2;
                res /= (mint)(r[i] - l[i]);
                return res;
            };

            mint tmp = 0;
            if((l[0] <= l[i]) && (r[0] <= r[i])){
                tmp += (mint)(l[i] - l[0]);
                tmp += func(l[i], r[0]);
            }
            else if((l[0] <= l[i]) && (r[0] >= r[i])){
                tmp += (mint)(l[i] - l[0]);
                tmp += func(l[i], r[i]);
            }
            else if((l[0] >= l[i]) && (r[0] <= r[i])){
                tmp += func(l[0], r[0]);
            }
            else if((l[0] >= l[i]) && (r[0] >= r[i])){
                tmp += func(l[0], r[i]);
            }
            tmp /= (mint)(r[0] - l[0]);
            ans += tmp;
        }
    }

    cout << ans << endl;
}