Problem:
Score: 300 points

Problem Statement

Find the minimum prime number greater than or equal to X.

Notes

A prime number is an integer greater than 1 that cannot be evenly divided by any positive integer except 1 and itself.

For example, 2, 3, and 5 are prime numbers, while 4 and 6 are not.

Constraints

2 \le X \le 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X

Output

Print the minimum prime number greater than or equal to X.

Sample Input 1

20

Sample Output 1

23

The minimum prime number greater than or equal to 20 is 23.

Sample Input 2

2

Sample Output 2

2

X itself can be a prime number.

Sample Input 3

99992

Sample Output 3

100003

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

internal static class CR
{
    public static string Get() { return Console.ReadLine(); }
    public static IEnumerable<string> GetTexts() { return Console.ReadLine().Split(' '); }
    public static int GetInteger() { return int.Parse(Console.ReadLine()); }
    public static IEnumerable<int> GetIntegers() { return Console.ReadLine().Split(' ').Select(x => int.Parse(x)); }
}

namespace AtCoderBeginnerContest
{
    internal class Program
    {
        public static int X { get; private set; }

        private static void Main() { var r = GetResult(); Debug.WriteLine(r); Console.WriteLine(r); }

        private static object GetResult()
        {
            X = CR.GetInteger();

            while (!IsPrime(X))
            {
                X++;
            }

            return X;
        }

        private static bool IsPrime(int x)
        {
            for (int i = x - 1; i > 1; i--)
            {
                if (x % i == 0) return false;
            }

            return true;
        }
    }
}