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)

def get_int
  gets.chop.to_i
end

def get_ints
  gets.chop.split.map(&:to_i)
end

def get_double
  gets.chop.to_f
end

def is_prime(x)
  if x == 2 or x == 3
    return true
  end
  if x % 2 == 0
    return false
  end
  3.step(Math.sqrt(x).to_i + 1, 2) do |i|
    if x % i == 0
      return false
    end
  end
  return true
end

def main
  x = get_int
  while true
    if is_prime(x)
      puts x
      exit 0
    end
    x += 1
  end
end

if __FILE__ == $0
  main
end