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;
class ProgramC
    {
        static void Main(string[] args)
        {
            
            //入力
            string input = Console.ReadLine();
            int x = int.Parse(input);
            int ans = 0;
            
            if(x == 3 || x == 2)
            {
                Console.WriteLine(x);
                return;
            }

            for(int i = x; i < 200000;i++)
            {
                int count = 0;
                for(int j = 2; j <= Math.Sqrt(i); j++)
                {
                    if(i % j != 0)
                        count++;
                    
                    if(count == (int)Math.Sqrt(i) - 1)
                    {
                        ans = i;
                    }
                }

                if(ans != 0)
                    break;
            }

            Console.WriteLine(ans);
        }
    }