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;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var X = Io.Read<int>();
            var i = X;
            while (true)
            {
                var isSosu = true;
                for (var j = 2; j < Math.Sqrt(i); j++)
                {
                    if (i % j == 0)
                    {
                        isSosu = false;
                        break;
                    }
                }

                if (isSosu)
                {
                    Io.Write(i.ToString());

                    break;
                }

                i++;
            }
        }

        static int NumberOfDigits(long x)
        {
            if (x < 10) return 1;

            var result = 0;
            while (x > 0)
            {
                result++;
                x /= 10;
            }

            return result;
        }

        static int SumOfDigits(int x)
        {
            var sum = 0;
            while (x > 0)
            {
                sum += x % 10;
                x /= 10;
            }

            return sum;
        }

        class Io
        {
            public static string Read()
            {
                return Console.ReadLine();
            }

            public static IEnumerable<string> ReadRepeat(int count)
            {
                return Enumerable.Range(0, count).Select(_ => Read());
            }

            public static T Read<T>()
            {
                return (T)Convert.ChangeType(Read(), typeof(T));
            }

            public static IEnumerable<T> ReadRepeat<T>(int count)
            {
                return Enumerable.Range(0, count).Select(_ => Read<T>());
            }

            public static string[] ReadList(char devide = ' ')
            {
                return Read().Split(devide);
            }

            public static T[] ReadList<T>(char devide = ' ')
            {
                return ReadList(devide)
                    .Select(s => (T)Convert.ChangeType(s, typeof(T)))
                    .ToArray();
            }

            public static IEnumerable<T[]> ReadListRepeat<T>(int count, char devide = ' ')
            {
                return Enumerable.Range(0, count).Select(_ => ReadList<T>(devide));
            }

            public static void Write(string value)
            {
                Console.WriteLine(value);
            }
        }
    }
}