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.Linq;

namespace PrimeNumber
{
    class Program
    {
        static void Main(string[] args)
        {

            var input = Console.ReadLine();
            long readNumber = int.Parse(input);
            bool isPrimeNumber = false;
            
            while(isPrimeNumber == false)
            {
                CountPrimeNumber(ref readNumber, ref isPrimeNumber);
            }

            Console.WriteLine(readNumber);                                 
        }

        static void CountPrimeNumber(ref long broughtNumber, ref bool isPrimeNumber)
        {
            isPrimeNumber = true;
            for (int i = 2; i < Math.Sqrt(broughtNumber); i++)
            {
                long primeNumber = broughtNumber % i;
                if (primeNumber == 0)
                {                    
                    isPrimeNumber = false;
                    broughtNumber++;
                    break;
                }                                
            }            
        }
    }
}