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 (1.42.0) (judge verdict: Accepted)

use whiteread::parse_line;

fn main() {
    let s: usize = parse_line().unwrap();
    let mut prime: Vec<bool> = vec![true; s * 2];
    prime[0] = false;
    prime[1] = false;

    for i in 0..s * 2 {
        if i as f64 > ((s * 2) as f64).sqrt() {
            break;
        }
        if prime[i] {
            for k in (i * 2..s * 2).step_by(i) {
                prime[k] = false;
            }
        }
    }
    for i in s..s * 2 {
        if prime[i] {
            println!("{}", i);
            break;
        }
    }
}