use std::collections::HashMap;

use proconio::input;

fn main() {
    input! {
        n:usize,
        m:usize,
        mut a:[usize;n],
    }

    a.sort();
    let mut poss = HashMap::new();
    for i in 0..n {
        poss.insert(a[i], i);
    }

    let mut seen = vec![false; n];
    seen[0] = true;
    let mut ans = vec![];
    for i in 1..n {
        if seen[i] {
            continue;
        }

        if m / a[i] > n {
            println!("-1");
            return;
        }

        for j in (1..).take_while(|&j| j * a[i] <= m) {
            let Some(pos)=poss.get(&(j*a[i]))else{
                println!("-1");
                return;
            };

            seen[*pos] = true;
        }
        ans.push(a[i]);
    }

    println!("{}", ans.len());
    for i in ans {
        print!("{} ", i);
    }
    println!()
}