using System;

public class Program
{
    private int N;
    private S[] LR;

    public void Solve()
    {
        var sc = new Scanner();
        N = sc.NextInt();
        LR = new S[N];
        for (int i = 0; i < N; i++)
        {
            LR[i] = new S(sc.NextInt(), sc.NextInt());
        }

        int lMax = -1;
        int rMin = int.MaxValue;

        int maxLen = -1;

        foreach (S s in LR)
        {
            lMax = Math.Max(lMax, s.L);
            rMin = Math.Min(rMin, s.R);
            maxLen = Math.Max(maxLen, s.R - s.L + 1);
        }

        int ans = -1;
        // 1 lMaxとrMinが同じグループ もしmaxLenが (lMax|rMin)な場合 -> 2
        {
            ans = Math.Max(0, rMin - lMax + 1) + maxLen;
        }
        // 2 違うグループ
        {
            Array.Sort(LR, (a, b) => a.L.CompareTo(b.L));
            var min = new int[N];
            int mn = int.MaxValue;
            for (int i = N - 1; i >= 0; i--)
            {
                mn = Math.Min(mn, LR[i].R);
                min[i] = mn;
            }

            for (int i = 0; i < N - 1; i++)
            {
                int a = Math.Max(0, rMin - LR[i].L + 1);
                int b = Math.Max(0, min[i + 1] - lMax + 1);
                ans = Math.Max(a + b, ans);
            }
        }
        Console.WriteLine(ans);
    }

    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

struct S
{
    public int L, R;

    public S(int l, int r)
    {
        L = l;
        R = r;
    }
}

class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}

Measured memory_bytes: 17420