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;
class C
{
    static void Main(string[] args)
    {
        long X = long.Parse(Console.ReadLine());
        long Y = 0;
        bool f = true;
        List<int> p = new List<int>();
        p.Add(2);
        if (X == 2)
        {
            Console.WriteLine(2);
            return;
        }
    
        for (int i = 2; f; i++)
        {
            for (int j = 0; j < p.Count; j++)
            {
                if (i % p[j] == 0)
                {   
                    break;
                }
                if (j == (p.Count - 1))
                {
                    p.Add(i);
                    if (X <= i)
                    {
                        Y = i;
                        f = false;
                    }
                }
            }
        }
        Console.WriteLine(Y);
    }
}