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;

namespace ABC149C
{
	class Program
	{
		static void Main(string[] args)
		{
			long a = long.Parse(Console.ReadLine());
			double sqrt = Math.Sqrt(a);
			bool flag = false;
			while (!flag)
			{
				if (a == 2) break;
				if (a % 2 == 0)
				{
					a++;
					continue;
				}
				for(int i = 3; i <= sqrt; i += 2)
				{
					flag = true;
					if (a % i == 0) 
					{
						flag = false;
						break;
					}
				}
				if (!flag) a++;
			}
			Console.WriteLine(a);
		}
	}
}