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;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    static class CNextPrime
    {
        static void Main(string[] args)
        {
            var x = long.Parse(Console.ReadLine());

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

            Console.WriteLine(x);
            Console.ReadLine();
        }

        static bool IsPrime(long x)
        {
            if (x < 2) return false;            
            if (x == 2) return true;
            if (x % 2 == 0) return false;

            for (long i = 3; i < x; i+=2)
            {
                if (x % i == 0) return false;
            }
            
            return true;
        }
    }
}