fn main() {
    let mut nmp = String::new();
    std::io::stdin().read_line(&mut nmp).ok();
    let nmp: Vec<usize> = nmp.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nmp[0];
    let m = nmp[1];
    let p = nmp[2];
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let maxval = *a.iter().max().unwrap();
    if maxval >= m {
        println!("1");
        return;
    }
    if a.iter().filter(|&&v| v % p > 0).count() == 0 {
        println!("-1");
        return;
    }
    let basemax= *a.iter().filter(|&&v| v % p > 0).max().unwrap();
    if basemax == 1 {
        println!("-1");
        return;
    }
    let mut cnt = 1;
    let mut x = maxval;
    while x < m {
        x *= basemax;
        cnt += 1;
    }
    println!("{}", cnt);
}