using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Numerics;

namespace Solver
{
    class Program
    {
        const int M = 1000000007;
        const double eps = 1e-9;
        static void Main()
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            var sc = new Scan();
            var s = sc.Str;
            var n = BigInteger.Parse(s);
            if (n < 26)
            {
                var p = int.Parse(s);
                switch (p)
                {
                    case 9:
                    case 10:
                    case 15:
                    case 16:
                    case 22:
                        Console.WriteLine(7);
                        return;
                    case 18:
                        Console.WriteLine(8);
                        return;
                    case 21:
                        Console.WriteLine(19);
                        return;
                    case 25:
                        Console.WriteLine(23);
                        return;
                }
                Console.WriteLine(p - 1);
                return;
            }
            if (n % 8 == 1 && isprime(n - 8))
            {
                Console.WriteLine(14);
                return;
            }
            sw.WriteLine(8);
            sw.Flush();
        }
        static BigInteger powmod(BigInteger a, BigInteger b, BigInteger M)
        {
            if (b == 0) return 1;
            if (b == 1) return a % M;

            var t = powmod(a, b / 2, M);

            if ((b & 1) == 0) return t * t % M;
            else return t * t * a % M;
        }

        static bool suspect(BigInteger a, int s, BigInteger d, BigInteger n)
        {
            BigInteger x = powmod(a, d, n);
            if (x == 1) return true;
            for (int r = 0; r < s; ++r)
            {
                if (x == n - 1) return true;
                x = x * x % n;
            }
            return false;
        }
        // {2,7,61,-1}                 is for n < 4759123141 (= 2^32)
        // {2,3,5,7,11,13,17,19,23,-1} is for n < 10^16 (at least)
        static bool isprime(BigInteger n)
        {
            if (n <= 1 || (n > 2 && n % 2 == 0)) return false;

            var test = new int[] { 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, -1 };
            BigInteger d = n - 1;
            int s = 0;
            while (d % 2 == 0)
            {
                ++s;
                d /= 2;
            }
            for (int i = 0; test[i] < n && test[i] != -1; ++i)
                if (!suspect(test[i], s, d, n))
                    return false;

            return true;
        }

        static string strsort(string s)
        {
            var c = s.ToCharArray();
            Array.Sort(c);
            return string.Join("", c);
        }
        static string strswap(string s, int i, int j)
        {
            var c = s.ToCharArray();
            c[i] = s[j];
            c[j] = s[i];
            return string.Join("", c);
        }

        static T[] copy<T>(T[] a)
        {
            var ret = new T[a.Length];
            for (int i = 0; i < a.Length; i++) ret[i] = a[i];
            return ret;
        }
    }
    class Scan
    {
        public int Int { get { return int.Parse(Console.ReadLine().Trim()); } }
        public long Long { get { return long.Parse(Console.ReadLine().Trim()); } }
        public string Str { get { return Console.ReadLine().Trim(); } }
        public int[] IntArr { get { return Console.ReadLine().Trim().Split().Select(int.Parse).ToArray(); } }
        public int[] IntArrWithSep(char sep) { return Console.ReadLine().Trim().Split(sep).Select(int.Parse).ToArray(); }
        public long[] LongArr { get { return Console.ReadLine().Trim().Split().Select(long.Parse).ToArray(); } }
        public double[] DoubleArr { get { return Console.ReadLine().Split().Select(double.Parse).ToArray(); } }
        public string[] StrArr { get { return Console.ReadLine().Trim().Split(); } }
        public List<int> IntList { get { return Console.ReadLine().Trim().Split().Select(int.Parse).ToList(); } }
        public List<long> LongList { get { return Console.ReadLine().Trim().Split().Select(long.Parse).ToList(); } }
        public void Multi(out int a, out int b) { var arr = IntArr; a = arr[0]; b = arr[1]; }
        public void Multi(out int a, out int b, out int c) { var arr = IntArr; a = arr[0]; b = arr[1]; c = arr[2]; }
        public void Multi(out int a, out int b, out int c, out int d) { var arr = IntArr; a = arr[0]; b = arr[1]; c = arr[2]; d = arr[3]; }
        public void Multi(out int a, out string b) { var arr = StrArr; a = int.Parse(arr[0]); b = arr[1]; }
        public void Multi(out int a, out int b, out string c) { var arr = StrArr; a = int.Parse(arr[0]); b = int.Parse(arr[1]); c = arr[2]; }
        public void Multi(out int a, out char b) { var arr = StrArr; a = int.Parse(arr[0]); b = arr[1][0]; }
        public void Multi(out char a, out int b) { var arr = StrArr; a = arr[0][0]; b = int.Parse(arr[1]); }
        public void Multi(out long a, out long b) { var arr = LongArr; a = arr[0]; b = arr[1]; }
        public void Multi(out long a, out int b) { var arr = LongArr; a = arr[0]; b = (int)arr[1]; }
        public void Multi(out string a, out string b) { var arr = StrArr; a = arr[0]; b = arr[1]; }
    }
    class mymath
    {
        const double eps = 1e-9;
        public long powmod(long a, long b, long M)
        {
            if (b == 0) return 1;
            if (b == 1) return a % M;

            var t = powmod(a, b / 2, M);

            if ((b & 1) == 0) return t * t % M;
            else return t * t % M * a % M;
        }
        public long gcd(long a, long b)
        {
            while (b != 0)
            {
                var t = a % b;
                a = b;
                b = t;
            }
            return a;
        }
        public long lcm(int a, int b) { return (a * b) / gcd(a, b); }
    }
}