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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;

fn main() {
    let mut i = parse_line::<u64>();
    loop {
        if is_prime(i) {
            println!("{}", i);
            break;
        } else {
            i += 1;
        }
    }
}
fn is_prime(n: u64) -> bool {
    for i in 2..n {
        if i.pow(2) >= n + 2 {
            break;
        }
        if n % i == 0 {
            return false;
        }
        if i * i > n {
            return true;
        }
    }
    true
}

fn parse_line<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}