E

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <bitset>
#include <queue>
#include <stack>
#include <sstream>
#include <cstring>
#include <numeric>
#include <ctime>
#include <cassert>
#include <random>
//#include <valarray>
//#include <fstream>

#define re return
#define fi first
#define se second
#define mp make_pair
#define pb emplace_back
#define all(x) x.begin(), x.end()
#define sz(x) ((int)(x).size())
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; i--)
#define y0 y32479
#define y1 y95874
#define next next239
#define prev prev239
#define fill(x, y) memset(x, y, sizeof(x))
#define sqr(x) ((x)*(x))
#define sqrt(x) sqrt(abs(x))
#define unq(x) (x.resize(unique(all(x)) - x.begin()))
#define ba back()
#define popcount __builtin_popcountll
#define firstbit(x) (63 - __builtin_clzll(x))
#define fastIO() {ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);}

#ifdef LOCAL_BOBER
bool local = true;
#define deb(x) cout << #x << " = " << (x) << endl
#define debn(x, n) { cout << #x << "(" << n << ") = " << \
    "{"; int _f_ = 1; rep(_i_, n) {if (!_f_) cout << "|"; cout << x[_i_]; _f_= 0;} cout << "}" << endl;}
#define deba(x) { cout << #x << " (size: " << sz(x) << ") = " << \
    "{"; int _f_ = 1; for (auto o : x) {if (!_f_) cout << "|"; cout << o; _f_ = 0;} cout << "}" << endl;}
#else
bool local = false;
#define deb(x) ;
#define debn(x, n) ;
#define deba(x) ;
#define endl "\n"
#endif

using namespace std;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<string> vs;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef pair<double, double> pdd;
typedef long double LD;
typedef double D;

template<class T> void print(T v) { cout << sz(v) << endl; for (auto x : v) cout << x << ' '; cout << endl; };
template<class T> void print1(T v) { cout << sz(v) << endl; for (auto x : v) cout << x + 1 << ' '; cout << endl; };
template<class T1, class T2> ostream& operator << (ostream &o, pair<T1, T2> x) {re o << x.fi << ' ' << x.se;}
template<class T1, class T2> istream& operator >> (istream &o, pair<T1, T2> &x) {re o >> x.fi >> x.se;}
template<class T> ostream& operator << (ostream &o, vector<T> &x) {for (auto &el : x) o << el << ' '; re o;}
template<class T> istream& operator >> (istream &o, vector<T> &x) {for (auto &el : x) o >> el; re o;}
template<class T1, class T2> pair<T1, T2> operator + (pair<T1, T2> a, pair<T1, T2> b) {a.fi += b.fi; a.se += b.se; re a;}
template<class T1, class T2> pair<T1, T2> operator - (pair<T1, T2> a, pair<T1, T2> b) {a.fi -= b.fi; a.se -= b.se; re a;}
template<class T1, class T2> void operator += (pair<T1, T2> &a, pair<T1, T2> b) {a.fi += b.fi; a.se += b.se;}
template<class T1, class T2> void operator -= (pair<T1, T2> &a, pair<T1, T2> b) {a.fi -= b.fi; a.se -= b.se;}

int nint() {int x; cin >> x; re x;}
double getTime() { re clock() / (double) CLOCKS_PER_SEC;};

mt19937 rnd(0);
int rand(int n) { re rnd() % n; }
int rand(int l, int r) { re rnd() % (r - l + 1) + l; }

//const int mod = 1000000000 + 7;
const int mod = 998244353;

void initIO() {
    if (local) {
        freopen("input.txt", "r", stdin);
        //freopen("output.txt", "w", stdout);
        srand((int)time(0));
        rnd.seed((int)time(0));
    }
    else {
        //freopen("input.txt", "r", stdin);
        //freopen("output.txt", "w", stdout);
        fastIO();
    }
}

void solve();
void precalc();

int TID;

signed main() {
    initIO();

    int tc = 1;
//  cin >> tc;

    precalc();
    rep(tt, tc) {
        TID = tt;
//      cout << "Case #" << tt + 1 << ": ";
        solve();
    }

    if (local)
        cout << endl << "time = " << getTime() << endl;
}

void precalc() {

}

/* ================ actual code starts here ================ */

int n;
int m;

int table[55][105][55];
int l1[55], r1[55];
int l[55], r[55];
vi v;

ll st(ll x, ll p) {
    ll ans = 1;
    while (p) {
        if (p & 1)
            ans = ans * x % mod;
        p /= 2;
        x = x * x % mod;
    }
    re ans;
}

ll get(int id, int k) {

    int len = v[id + 1] - v[id];

    len += k;
    ll ans = 1;
    for (int i = 1; i <= k; i++) {
        ans = ans * (len - i) % mod;
        ans = ans * st(i, mod - 2) % mod;
    }
//  cout << id << ' ' << k << ' ' << ans << endl;
    re ans;
}

int getans(int p, int id, int k) {
    int &ans = table[p][id][k];
    if (ans != -1)
        re ans;

//  cout << p << ' ' << id << ' ' << k << endl;
    if (p == n) {
        ans = get(id, k);
        re ans;
    }

    ans = 0;
    ll tmp = get(id, k);
    if (id == 0)
        tmp = 1;
    deb(tmp);
    for (int i = id + 1; i < r1[p]; i++) {
        if (i < l1[p])
            continue;
        ans += getans(p + 1, i, 1) * tmp % mod;
        if (ans >= mod)
            ans -= mod;
    }
    if (id < r1[p] && id >= l1[p]) {
        ans += getans(p + 1, id, k + 1);
        if (ans >= mod)
            ans -= mod;
    }
    re ans;
}

void solve() {
    cin >> n;
    v.pb(-1);
    rep(i, n) {
        cin >> l[i] >> r[i];
        r[i]++;
        v.pb(l[i]);
        v.pb(r[i]);
    }
    sort(all(v));
    unq(v);
    deba(v);
    rep(i, n) {
        l1[i] = lower_bound(all(v), l[i]) - v.begin();
        r1[i] = lower_bound(all(v), r[i]) - v.begin();
//      cout << i << ' ' << l1[i] << ' ' << r1[i] << endl;
    }
    fill(table, -1);
    cout << getans(0, 0, 1);
}