#[macro_use]
mod input_mcr {
    // ref: tanakh <https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8>
    // diff: using Parser
    #[macro_export(local_inner_macros)]
    macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut parser = Parser::from_str($s);
        input_inner!{parser, $($r)*}
    };
    (parser = $parser:ident, $($r:tt)*) => {
        input_inner!{$parser, $($r)*}
    };
    (new_stdin_parser = $parser:ident, $($r:tt)*) => {
        let stdin = std::io::stdin();
        let reader = std::io::BufReader::new(stdin.lock());
        let mut $parser = Parser::new(reader);
        input_inner!{$parser, $($r)*}
    };
    ($($r:tt)*) => {
        input!{new_stdin_parser = parser, $($r)*}
    };
}

    #[macro_export(local_inner_macros)]
    macro_rules! input_inner {
    ($parser:ident) => {};
    ($parser:ident, ) => {};
    ($parser:ident, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($parser, $t);
        input_inner!{$parser $($r)*}
    };
}

    #[macro_export(local_inner_macros)]
    macro_rules! read_value {
    ($parser:ident, ( $($t:tt),* )) => {
        ( $(read_value!($parser, $t)),* )
    };
    ($parser:ident, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($parser, $t)).collect::<Vec<_>>()
    };
    ($parser:ident, chars) => {
        read_value!($parser, String).chars().collect::<Vec<char>>()
    };
    ($parser:ident, char_) => {
        read_value!($parser, String).chars().collect::<Vec<char>>()[0]
    };
    ($parser:ident, usize1) => {
        read_value!($parser, usize) - 1
    };
    ($parser:ident, i64_) => {
        $parser.fast_i64()
    };
    ($parser:ident, usize_) => {
        $parser.fast_i64() as usize
    };
    ($parser:ident, usize1_) => {
        ($parser.fast_i64() - 1) as usize
    };
    ($parser:ident, $t:ty) => {
        $parser.next::<$t>().expect("Parse error")
    };
}

    use std::io;
    use std::io::BufRead;
    use std::str;

    // ref: tatsuya6502 <https://qiita.com/tatsuya6502/items/cd448486f7ef7b5b8c7e>
    // ref: wariuni <https://qiita.com/tatsuya6502/items/cd448486f7ef7b5b8c7e#comment-7040a5ae96305e884eb9>
    // diff: using std::io::BufRead::fill_buf()
    pub struct Parser<R> {
        pub reader: R,
        buf: Vec<u8>,
        pos: usize,
    }

    impl Parser<io::Empty> {
        pub fn from_str(s: &str) -> Parser<io::Empty> {
            Parser {
                reader: io::empty(),
                buf: s.as_bytes().to_vec(),
                pos: 0,
            }
        }
    }

    impl<R: BufRead> Parser<R> {
        pub fn new(reader: R) -> Parser<R> {
            Parser {
                reader: reader,
                buf: vec![],
                pos: 0,
            }
        }
        pub fn update_buf(&mut self) {
            self.buf.clear();
            self.pos = 0;
            loop {
                let (len, complete) = {
                    let buf2 = self.reader.fill_buf().unwrap();
                    self.buf.extend_from_slice(buf2);
                    let len = buf2.len();
                    (len, buf2[len - 1] <= 0x20)
                };
                self.reader.consume(len);
                if complete {
                    break;
                }
            }
        }
        pub fn next<T: str::FromStr>(&mut self) -> Result<T, T::Err> {
            loop {
                let mut begin = self.pos;
                while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                    begin += 1;
                }
                let mut end = begin;
                while end < self.buf.len() && (self.buf[end] > 0x20) {
                    end += 1;
                }
                if begin != self.buf.len() {
                    self.pos = end;
                    return unsafe { str::from_utf8_unchecked(&self.buf[begin..end]) }.parse::<T>();
                } else {
                    self.update_buf();
                }
            }
        }
        pub fn fast_i64(&mut self) -> i64 {
            loop {
                let mut begin = self.pos;
                while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                    begin += 1;
                }
                if begin == self.buf.len() {
                    self.update_buf();
                    continue;
                }
                let mut res = 0;
                let (is_positive, mut end) = match self.buf[begin] {
                    b'+' => (true, begin + 1),
                    b'-' => (false, begin + 1),
                    _ => (true, begin),
                };
                while end < self.buf.len() && (self.buf[end] > 0x20) {
                    res = res * 10 + (self.buf[end] as i64 - '0' as i64);
                    end += 1;
                }
                if begin != self.buf.len() {
                    self.pos = end;
                    return if is_positive { res } else { -res };
                } else {
                    self.update_buf();
                }
            }
        }
    }
}

use input_mcr::*;
use std::cmp::*;

use std::collections::BinaryHeap;

/*
#[derive(Debug)]
pub struct MinHeapWithOffset {
    q: MinHeap<i64>,
    offset: i64,
}

impl MinHeapWithOffset {
    pub fn new() -> MinHeapWithOffset {
        MinHeapWithOffset {
            q: BinaryHeap::new(),
            offset: 0,
        }
    }
    pub fn all_add(&mut self, x: i64) {
        self.offset += x;
    }
    pub fn min(&self) -> i64 {
        self.q.peek().unwrap().0 + self.offset
    }
    pub fn pop(&mut self) -> i64 {
        self.q.pop().unwrap().0 + self.offset
    }
    pub fn push(&mut self, x: i64) {
        self.q.push(Reverse(x - self.offset))
    }
}
*/

fn f(ys: &Vec<(usize, usize)>, n: usize, m: usize, v: usize, p: usize, i: usize) -> bool {
    if i < p {
        return true;
    }
    if i >= n {
        return false;
    }
    if ys[p - 1].0 > ys[i].0 + m {
        return false;
    }
    let mut zs = vec![];
    for k in p - 1..n {
        if k != i {
            zs.push(ys[i].0 + m - ys[k].0);
        }
    }
    zs.reverse();
    if (v - 1) <= (p - 1) {
        return true;
    }
    let w = (v - 1) - (p - 1);
    let mut rem = m as i64;
    //let mut q = MinHeapWithOffset::new();
    let mut t = 0;
    for &z in &zs {
        t += min(m, z);
    }
    return t >= w * m;
    /*
    if t >= w * m {

    }
    // eprintln!("zs = {:?}", zs);
    for i in 0..w {
        q.push(zs[i] as i64);
    }
    for i in w..zs.len() {
        // eprintln!("q = {:?}", q);
        if q.min() < 0 {
            return false;
        }
        let top = q.pop();
        q.all_add(top);
        rem -= top as i64;
        if rem <= 0 {
            return true;
        }
        q.push(zs[i] as i64);
    }
    false
    */
}

fn main() {
    input! {
        n: usize,
        m: usize,
        v: usize,
        p: usize,
        xs: [usize; n],
    }
    let mut ys: Vec<(usize, usize)> = xs.iter().enumerate().map(|(i, &x)| (x, i)).collect();
    ys.sort();
    ys.reverse();
    let mut res = 0;
    for i in (0..20).rev() {
        let t = res + (1 << i);
        // eprintln!("bin_t = {}", t);
        if f(&ys, n, m, v, p, t) {
            res = t;
        }
    }
    res += 1;
    /*
    let mut res = 0;
    res += p;
    let cu = {
        let mut cu = 0;
        for i in p-1..n {
            cu += ys[i].0;
        }
        cu
    };
    let border = ys[p-1].0;
    // eprintln!("border = {}", border);
    for i in p..n {
        if ys[i].0 + m >= border {
            if v-1 >= p-1 {
                let w_border_r = n - (v - 1 - (p-1));
                let w_border_l = w_border_r - 1;
                // eprintln!("w_l = {}, w_r = {}", w_border_l, w_border_r);
                if i <= w_border_l {
                    if w_border_r < n && ys[w_border_r].0 + 1 > ys[i].0 + m {
                        continue;
                    }
                }
                else {
                    if w_border_l < n && ys[w_border_l].0 + 1 > ys[i].0 + m {
                        continue;
                    }
                }
                let rem = (v-1 - (p-1)) * m;
                if (n-p) * (ys[i].0 + m) - (cu - ys[i].0) >= rem {
                    res += 1;
                }
            }
        }
    }
    */
    println!("{}", res);
}



Measured memory_bytes: 11440