using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var map = NArr(n);
        var mod = 998_244_353;
        var ans = 1L;
        var len = map[0][1] - map[0][0] + 1L;
        for (var i = 1; i < n; ++i)
        {
            var pa = Exp(len * (map[i][1] - map[i][0] + 1), mod - 2, mod);
            var ch = 0L;
            if (map[0][1] < map[i][1])
            {
                ch += len * (map[i][1] - Math.Max(map[i][0] - 1, map[0][1])) % mod;
            }
            {
                var left = Math.Max(map[0][0], map[i][0]);
                var right = Math.Min(map[0][1], map[i][1]);
                if (left < right) ch += (right - left + 1L) * (right - left) / 2 % mod;
            }
            ans = (ans + pa * (ch % mod) % mod) % mod;
        }
        WriteLine(ans);
    }
    static long Exp(long n, long p, int mod)
    {
        long _n = n % mod;
        var _p = p;
        var result = 1L;
        if ((_p & 1) == 1) result *= _n;
        while (_p > 0)
        {
            _n = _n * _n % mod;
            _p >>= 1;
            if ((_p & 1) == 1) result = result * _n % mod;
        }
        return result;
    }
}