using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using static System.Console;
using static System.Math;
using static MyIO;
using static MyUtil;

public class B { public static void Main() => (new Solver()).Solve(); }

public class Solver
{
	public void Solve()
	{
		long N = GetLong();
		var L = new long[N];
		var R = new long[N];
		for(long i = 0; i < N; i++)
		{
			L[i] = GetLong();
			R[i] = GetLong() + 1;
		}

		long lmax = long.MinValue;
		long rmin = long.MaxValue;
		long p = -1;
		long q = -1;
		for(long i = 0; i < N; i++)
		{
			if(L[i] > lmax)
			{
				lmax = L[i];
				p = i;
			}
			if(R[i] < rmin)
			{
				rmin = R[i];
				q = i;
			}
		}

		long z = 0;
		var list = new List<(long, long)>();
		for(long i = 0; i < N; i++)
		{
			list.Add((Max(0, R[i] - lmax), Max(0, rmin - L[i])));
			chmax(ref z, R[i] - L[i]);
		}
		list.Sort((x, y) => x.Item1 != y.Item1 ? x.Item1.CompareTo(y.Item1) : y.Item2.CompareTo(x.Item2));

		var ast = new SegmentTree<long>(N, long.MaxValue, (x, y) => Min(x, y));
		var bst = new SegmentTree<long>(N, long.MaxValue, (x, y) => Min(x, y));
		for(long i = 0; i < N; i++)
		{
			ast.Update(i, list[(int)i].Item1);
			bst.Update(i, list[(int)i].Item2);
		}

		long ans = Max(0, rmin - lmax) + z;
		for(long i = 0; i < N - 1; i++)
			chmax(ref ans, bst.Query(0, i + 1) + ast.Query(i + 1, N));

		WriteLine(ans);
	}
}

public class SegmentTree<T>
{
	private long N;
	private T INI;
	private Func<T, T, T> Func;
	private T[] dat;

	public T this[long index]
	{
		get { return dat[index + N - 1]; }
		set { Update(index, value); }
	}

	public SegmentTree(long n, T ini, Func<T, T, T> func)
	{
		N = 1;		
		while(N < n)
			N <<= 1;

		INI = ini;
		Func = func;
			
		dat = new T[2 * N - 1];
		for(long i = 0; i < 2 * N - 1; i++)
			dat[i] = INI;
	}

	public void Update(long k, T a)
	{
		k += N - 1;
		dat[k] = a;
		while(k > 0)
		{
			k = (k - 1) / 2;
			dat[k] = Func(dat[k * 2 + 1], dat[k * 2 + 2]);
		}
	}

	public T Query(long a, long b, long k = 0, long l = 0, long r = -1)
	{
		if(r == -1)
			r = N;

		if(r <= a || b <= l)
			return INI;

		if(a <= l && r <= b)
			return dat[k];
		else
		{
			T vl = Query(a, b, k * 2 + 1, l, (l + r) / 2);
			T vr = Query(a, b, k * 2 + 2, (l + r) / 2, r);
			return Func(vl, vr);
		}
	}
}

public static class MyIO
{
	private static string[] args = new string[0];
	private static int cnt = 0;
	private static IEnumerable<string> getArgs(long N) => Range(0, N).Select(_ => getArg());
	private static string getArg()
	{
		if(cnt == args.Length) { args = Console.ReadLine().Split(); cnt = 0; }
		return args[cnt++];
	}

	public static int GetInt() => int.Parse(getArg());
	public static long GetLong() => long.Parse(getArg());
	public static double GetDouble() => double.Parse(getArg());
	public static decimal GetDecimal() => decimal.Parse(getArg());
	public static string GetString() => getArg();
	public static char GetChar() => getArg()[0];
	public static int[] GetInts(long N) => getArgs(N).Select(int.Parse).ToArray();
	public static long[] GetLongs(long N) => getArgs(N).Select(long.Parse).ToArray();
	public static double[] GetDoubles(long N) => getArgs(N).Select(double.Parse).ToArray();
	public static decimal[] GetDecimals(long N) => getArgs(N).Select(decimal.Parse).ToArray();
	public static string[] GetStrings(long N) => getArgs(N).ToArray();
}

public static class MyUtil
{
	public static void chmax<T>(ref T x, T y) where T : IComparable<T> { if(x.CompareTo(y) < 0) x = y; }
	public static void chmin<T>(ref T x, T y) where T : IComparable<T> { if(x.CompareTo(y) > 0)	x = y; }
	public static void swap<T>(ref T x, ref T y) { T tmp = x; x = y; y = tmp; }
	public static long rightShift(long x, long y) => (x >> (int)y);
	public static long leftShift(long x, long y) => (x << (int)y);
	public static bool contains(long s, long x) => (rightShift(s, x) & 1L) == 1L;
	public static long gcd(long x, long y) => (y == 0) ? x : gcd(y, x % y);
	public static long lcm(long x, long y) => (x / gcd(x,y)) * y;	
	public static IEnumerable<int> Range(long start, long count) => Enumerable.Range((int)start, (int)count);
	public static void Sort(this List<string> source) => source.Sort(StringComparer.Ordinal);
}


Measured memory_bytes: 50200