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 ConsoleApp45 {
    class Program {
        static int ans;

        static void Main(string[] args) {
            int X = int.Parse(Console.ReadLine());

            //解答
            ans = X;

            bool loop = true;

            while (loop) {
                //Xが素数なら
                if (isPrime(ans)) {
                    //ループを抜ける
                    loop = false;
                } else {
                    //Xに1を足して次のループへ
                    ans++;
                }
            }
            Console.WriteLine(ans);
        }

        static bool isPrime(int X) {
            for (int i = 2; i <= Math.Sqrt(X); i++) {
                if ((ans % i) == 0) {
                    return false;
                }
            }
            return true;
        }
    }
}