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 Ruby (2.3.3) (judge verdict: Accepted)

x = gets.to_i

def is_prime(n)
    a = Math.sqrt(n).to_i + 1
    if n == 2
        return true
    elsif n % 2 == 0
        return false
    else
        i = 3
        while i < a
            if n % i == 0
                return false
            end
            i += 2
        end
        return true
    end
end

while true
    if is_prime(x)
        puts x
        break
    end
    x += 1
end