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.Linq;
using System.Collections.Generic;
class Program
{
	static void Main(string[] args)
	{
	    int x = IO.GetInt();
	    
	    bool isPrime = IsPrime(x);
	    while(!isPrime){
	        x++;
	        isPrime = IsPrime(x);
	    }
	    
	    
	    Console.WriteLine(x);
	    
	}
	
	static bool IsPrime(int x){
	    if(x==2)return true;
	    for(int i=2;i<Math.Sqrt((double)x);i++){
	        if(x%i==0)return false;
	    }
	    return true;
	}
    
}

static class IO
{
    static public string GetString() { return Console.ReadLine(); }
    static public int GetInt() { return int.Parse(Console.ReadLine()); }
    static public long GetLong() { return long.Parse(Console.ReadLine()); }
    static public List<string> GetStringList() { return Console.ReadLine().Split(' ').ToList(); }
    static public List<int> GetIntList() { return Console.ReadLine().Split(' ').Select(int.Parse).ToList(); }
    static public List<long> GetLongList() { return Console.ReadLine().Split(' ').Select(long.Parse).ToList(); }
    static public List<double> GetDoubleList() { return Console.ReadLine().Split(' ').Select(double.Parse).ToList(); }
    static public void WriteStrings<T>(IEnumerable<T> values) { foreach (var o in values) { Console.Write(o + " "); } }
}