use std::collections::BTreeMap;

fn main() {
    let (n, k, x, y) = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        (
            iter.next().unwrap().parse::<u64>().unwrap(),
            iter.next().unwrap().parse::<u64>().unwrap(),
            iter.next().unwrap().parse::<u64>().unwrap(),
            iter.next().unwrap().parse::<u64>().unwrap(),
        )
    };

    let a: Vec<u64> = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        buf.split_whitespace().map(|x| x.parse().unwrap()).collect()
    };

    let mut map: BTreeMap<u64, u64> = BTreeMap::new();

    for x in a {
        let count = map.entry((x + k - 2) / k).or_insert(0);
        *count += 1;
    }

    let mut ans: u64 = 0;
    let mut sum: u64 = n;
    let mut healed: u64 = 0;
    let heal_more: u64 = y / x;

    for (heal, count) in map {
        if sum <= heal_more {
            ans += x * sum * (heal - healed);
        } else {
            ans += y * (heal - healed);
        }

        sum -= count;
        healed = heal;
    }

    println!("{}", ans);
}