fn run<'a, I, W>(mut scanner: I, mut writer: W)
where
    I: Iterator<Item = &'a str>,
    W: std::io::Write,
{
    macro_rules! scan {
        ([$t:tt; $n:expr]) => ((0..$n).map(|_| scan!($t)).collect::<Vec<_>>());
        (($($t:tt),*)) => (($(scan!($t)),*));
        (Usize1) => (scan!(usize) - 1);
        (Bytes) => (scan!(String).into_bytes());
        ($t:ty) => (scanner.next().unwrap().parse::<$t>().unwrap());
    }
    macro_rules! input {
        ($($($v:ident)* : $t:tt),* $(,)?) => ($(let $($v)* = scan!($t);)*);
    }
    macro_rules! println {
        ($($arg:tt)*) => (writeln!(writer, $($arg)*).ok());
    }
    
    for _ in 0..scan!(usize) {
        input! {
            n: i64, a: i64, w: i64, k: i64,
        }

        if n == 1 {
            println!("{}", a - (1 + w) * w / 2);
        } else if k == 1 {
            println!("{}", a);
        } else if k < n {
            if a < k - 1 {
                if w > n - k {
                    println!("-1");
                } else {
                    println!(":(");
                }
            } else {
                let x = a / k;
                if (x + 1) * (k - 1) + x <= a {
                    println!("{}", x);
                } else {
                    println!("{}", x - 1);
                }
            }
        } else {
            let mut a = a;
            let mut w = w;

            let mut i = 1;
            while w >= n && i * n <= a {
                a -= i * n;
                w -= n;
                i += 1;
            }

            if i * w <= a {
                a -= i * w;
                let x = a / k;
                if (x + 1) * (k - 1) + x <= a {
                    println!("{}", x);
                } else {
                    println!("{}", x - 1);
                }
            } else {
                while a - i >= 0 {
                    a -= i;
                    w -= 1;
                }
                println!("{}", a - (i + (i + w - 1)) * w / 2);
            }
        }
    }
}

fn main() {
    let ref mut buf = Vec::new();
    std::io::Read::read_to_end(&mut std::io::stdin(), buf).ok();
    let scanner = unsafe {
        std::str::from_utf8_unchecked(buf).split_ascii_whitespace()
    };

    let stdout = std::io::stdout();
    let writer = std::io::BufWriter::new(stdout.lock());

    run(scanner, writer);
}