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: Runtime Error)

using System;
using System.Linq;

namespace Next_Prime
{
    class Program
    {
        static void Main(string[] args)
        {
            const int MAX_PRIME = 10004;
            var input = long.Parse(Console.ReadLine());
            var primeArray = Enumerable.Repeat<bool>(true, MAX_PRIME).ToArray();
            primeArray[0] = false;
            primeArray[1] = false;
            for(var i = 2; i < input; i++)
            {
                if(primeArray[i])
                {
                    var maxJ = MAX_PRIME / i;
                    for (var j = 1; j < maxJ; j++)
                    {
                        primeArray[i * j] = false;
                    }
                }
            }
            var minPrime = primeArray.ToList().IndexOf(true);
            Console.WriteLine(minPrime);
        }
    }
}