#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

void solve(){
    
}

int main(){
    int n; cin >> n;
    vvi v(n, vi(2)); rep(i, n)rep(j, 2)cin >> v[i][j];
    if(n == 1){
        cout << 1 << endl;
        return 0;
    }
    mint ans = mint(1);
    int l = v[0][0], r = v[0][1];
    rep2(i, 1, n){
        if(v[i][1] <= l)continue;
        if(v[i][0] > r){
            ans++;
            continue;
        }
        int st = max(l, v[i][0]);
        int en = min(r, v[i][1]);
        int st2 = st - v[i][0] + 1, en2 = en - v[i][0] + 1;
        mint p = mint(st2 + en2)*mint(en-st+1)/(mint(2)*mint(v[i][1]- v[i][0]+1)*mint(r-l+1));
        if(en < r)p += mint(r - en)/mint(r-l+1);
        ans += 1 - p;
    }cout << ans.val() << endl;

    return 0;
}