use std::cmp::min;

fn main() {
    let mut nkxy = String::new();
    std::io::stdin().read_line(&mut nkxy).ok();
    let nkxy: Vec<usize> = nkxy.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nkxy[0];
    let k = nkxy[1];
    let x = nkxy[2];
    let y = nkxy[3];
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let mut a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse::<usize>().unwrap() - 1).collect();

    a.sort();
    if x >= y {
        let result = (a[n-1] / k + if a[n-1] % k > 0 { 1 } else { 0 }) * y;
        println!("{}", result);
    } else {
        let people = min(y / x, n);
        if people == n {
            println!("{}", a.iter().map(|&i| i / k + if i % k > 0 { 1 } else { 0 }).sum::<usize>() * x);
        } else {
            let mut result: usize = 0;
            let base = a[n-1-people] / k + if a[n-1-people] % k > 0 { 1 } else { 0 };
            result += base * y;
            let rest: usize = a.iter().skip(n - people)
                .map(|&i| if i <= base * k { 0 } else { (i - base * k) / k + if (i - base * k) % k > 0 { 1 } else { 0 } })
                .sum()
            ;
            result += rest * x;
            println!("{}", result);
        }
    }
}