namespace AtCoder;

#nullable enable

using System.Numerics;

readonly record struct ModInt :
    IEqualityOperators<ModInt, ModInt, bool>,
    IAdditiveIdentity<ModInt, ModInt>,
    IAdditionOperators<ModInt, ModInt, ModInt>,
    IUnaryNegationOperators<ModInt, ModInt>,
    ISubtractionOperators<ModInt, ModInt, ModInt>,
    IMultiplicativeIdentity<ModInt, ModInt>,
    IMultiplyOperators<ModInt, ModInt, ModInt>,
    IDivisionOperators<ModInt, ModInt, ModInt>
{
    int V { get; init; }
    public const int Mod = 998244353;
    public ModInt(long value)
    {
        var v = value % Mod;
        if (v < 0) v += Mod;
        V = (int)v;
    }
    ModInt(int value) { V = value; }

    public static implicit operator ModInt(long v) => new(v);
    public static implicit operator int(ModInt modInt) => modInt.V;
    public static ModInt operator +(ModInt a, ModInt b)
    {
        var v = a.V + b.V;
        if (v >= Mod) v -= Mod;
        return new(v);
    }
    public static ModInt operator -(ModInt a) => new(a.V == 0 ? 0 : Mod - a.V);
    public static ModInt operator -(ModInt a, ModInt b)
    {
        var v = a.V - b.V;
        if (v < 0) v += Mod;
        return new(v);
    }
    public static ModInt operator *(ModInt a, ModInt b) => new((int)((long)a.V * b.V % Mod));
    public static ModInt operator /(ModInt a, ModInt b)
    {
        if (b == 0) throw new DivideByZeroException();
        var (d, x, _) = ExtendedGcd(b.V, Mod);
        if (d > 1) throw new DivideByZeroException();
        return x * a.V;
    }

    public ModInt Power(long p)
    {
        if (p < 0) return (MultiplicativeIdentity / V).Power(-p);
        long res = 1;
        long k = V;
        while (p > 0)
        {
            if ((p & 1) > 0) res = res * k % Mod;
            k = k * k % Mod;
            p >>= 1;
        }
        return res;
    }

    static (long d, long x, long y) ExtendedGcd(long a, long b)
    {
        if (b == 0) return (a, 1, 0);
        var (d, x, y) = ExtendedGcd(b, a % b);
        return (d, y, x - a / b * y);
    }

    public static ModInt AdditiveIdentity => new(0);
    public static ModInt MultiplicativeIdentity => new(1);

    public override string ToString() => V.ToString();
}

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}

class AtCoder
{
    object? Solve()
    {
        var n = Int();
        var pz = n.Repeat(() => (Int(), Int()));
        ModInt ans = 0;
        var (l0, r0) = pz[0];
        var invd = (ModInt)1 / (r0 - l0 + 1);
        for (var i = 1; i < n; i++)
        {
            var (l, r) = pz[i];
            ModInt ins = 0;
            if (r > r0) ins += r - Math.Max(r0, l - 1);
            long ml = Math.Max(l0, l) - l0 - 1;
            long mr = Math.Min(r0, r) - l0;
            if (mr >= 0) ins += mr * (mr + 1) / 2 * invd;
            if (ml >= 0) ins -= ml * (ml + 1) / 2 * invd;
            ans += ins / (r - l + 1);
        }
        return ans + 1;
    }

    public static void Main() => new AtCoder().Run();
    public void Run()
    {
        var res = Solve();
        if (res != null)
        {
            if (res is bool yes) res = yes ? "Yes" : "No";
            sw.WriteLine(res);
        }
        sw.Flush();
    }

    string[] input = Array.Empty<string>();
    int iter = 0;
    readonly StreamWriter sw = new(Console.OpenStandardOutput()) { AutoFlush = false };

    string String()
    {
        while (iter >= input.Length) (input, iter) = (Console.ReadLine()!.Split(' '), 0);
        return input[iter++];
    }
    T Input<T>() where T : IParsable<T> => T.Parse(String(), null);
    int Int() => Input<int>();
    void Out(object? x, string? separator = null)
    {
        separator ??= Environment.NewLine;
        if (x is System.Collections.IEnumerable obj and not string)
        {
            var firstLine = true;
            foreach (var item in obj)
            {
                if (!firstLine) sw.Write(separator);
                firstLine = false;
                sw.Write(item);
            }
        }
        else sw.Write(x);
        sw.WriteLine();
    }
}