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 AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int X = int.Parse(Console.ReadLine());
            bool tmp = true;
            int a = X - 1;
            while (tmp)
            {
                a += 1;
                tmp = hantei(a);
            }
            Console.WriteLine(a);
        }

        static bool hantei(int x)
        {
            bool flag = false;
            for(int i = 2; i < x; i++)
            {
                if(x % i == 0)
                {
                    flag = true;
                    break;
                }
            }
            return flag;
        }
       
    }
}
/*
long a, b, c;
a = long.Parse(Console.ReadLine()); //標準入力
string[] str = Console.ReadLine().Split(' ');//2つ以上のスペース区切り入力の取得
b = long.Parse(str[0]);  //数値で受け取りたい場合は変換する
c = long.Parse(str[1]);
string S = Console.ReadLine();
char[] C = new char[N];
C = S.ToCharArray();
Console.Write("改行なし a = {0} b = {1} c = {2}", a, b, c)//改行なし出力
Console.WriteLine("改行あり a = {0} b = {1} c = {2}", a, b, c);//改行付き出力
Member = ReadLine().Split(' ').Select(long.Parse).ToArray();

string[] str = Console.ReadLine().Split(' ');
long[] a = new long[N];
for(long i = 0; i < N; i++) a[i] = long.Parse(str[i]);
 */
/*
      static long func(long n)
      {
          long d = 0;
          for (long i = 0; i < 10; i++)
          {
              if (n / longPow(10, i) == 0)
              {
                  d = i;
                  break;
              }
          }
          long ret = A * n + B * d;
          return ret;
      }
      static long longPow(long a, long n)
      {
          long b = 1;
          for (long i = 0; i < n; i++) b = b * a;
          return b;
      }
      */