use std::io::*;
use std::str::FromStr;

fn main() {
    let inputs = (0..4).map(|_| read()).collect::<Vec<i64>>();
    exec(inputs);
}

fn exec(inputs: Vec<i64>) {
    if inputs[1] / inputs[2] <= inputs[0] {
        rec_yasai(inputs[1] / inputs[2], inputs);
    } else {
        rec_yasai(inputs[0], inputs);
    }
}

fn rec_yasai(max_yasai: i64, inputs: Vec<i64>) {
    if max_yasai == 0 || max_yasai + (inputs[2] * 2) < inputs[3] {
        return println!("{}", max_yasai);
    } else {
        rec_yasai(max_yasai - 1, inputs);
    }
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}