//https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

//

fn run() {
    input! {
        n: usize,
        k: u64,
        x: u64,
        y: u64,
        a: [u64; n],
    }
    let mut a = a;
    for a in a.iter_mut() {
        *a = (*a - 1 + k - 1) / k;
    }
    a.sort();
    let mut ans = a[n - 1] * y;
    let mut sum = 0;
    for (i, a) in a.windows(2).rev().enumerate() {
        sum += a[1];
        let c = (i + 1) as u64;
        let cost = (sum - a[0] * c).saturating_mul(x);
        ans = std::cmp::min(ans, (a[0] * y).saturating_add(cost));
    }
    sum += a[0];
    ans = std::cmp::min(ans, sum.saturating_mul(x));
    println!("{}", ans);
}

fn main() {
    run();
}