use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let m: usize = itr.next().unwrap().parse().unwrap();
    let p: usize = itr.next().unwrap().parse().unwrap();
    let a: Vec<usize> = (0..n)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();

    let mut max1 = 0;
    let mut max2 = 0;
    for &e in a.iter() {
        max1 = std::cmp::max(max1, e);
        if e % p != 0 {
            max2 = std::cmp::max(max2, e);
        }
    }
    
    if max1 > m {
        println!("{}", 1);
    } else if max2 <= 1 {
        println!("-1");
    } else {
        let mut now = 1;
        let mut ans = 0;
        while max1 * now <= m {
            ans += 1;
            now *= max2;
        }
        println!("{}", ans + 1);
    }
}