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;

namespace c
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            foreach(var i in GetPrimeNumber(1000000)){
                if(i >= n){
                    Console.WriteLine(i);
                    break;
                }
            }
        }

        static IEnumerable<long> GetPrimeNumber(long n){
            if(n < 2){
               yield return 0;
            }

            if(n >= 2){
                yield return 2;
            }

            for(var i = 3; i <= n; i += 2){
                var flag = true;
                var sqrtnum = Math.Sqrt(i);
                for(var j = 3; j <= sqrtnum; j += 2){
                    if(i % j == 0){
                        flag = false;
                        break;
                    }
                }
                if(flag){
                    yield return i;
                }
            }
        }
    }
}