package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func getNextString(scanner *bufio.Scanner) string {
	if !scanner.Scan() {
		panic("scan failed")
	}
	return scanner.Text()
}
func atoi(s string) int                             { x, _ := strconv.Atoi(s); return x }
func getNextInt(scanner *bufio.Scanner) int         { return atoi(getNextString(scanner)) }
func atoi64(s string) int64                         { x, _ := strconv.ParseInt(s, 10, 64); return x }
func getNextInt64(scanner *bufio.Scanner) int64     { return atoi64(getNextString(scanner)) }
func atof64(s string) float64                       { x, _ := strconv.ParseFloat(s, 64); return x }
func getNextFloat64(scanner *bufio.Scanner) float64 { return atof64(getNextString(scanner)) }
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	extra := 0
	if os.Getenv("I") == "IronMan" {
		fp, _ = os.Open(os.Getenv("END_GAME"))
		extra = 100
	}
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
	writer := bufio.NewWriter(wfp)
	defer func() {
		r := recover()
		if r != nil {
			fmt.Fprintln(writer, r)
		}
		writer.Flush()
	}()
	solve(scanner, writer)
	for i := 0; i < extra; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
}

const Inf = 1000_000_000_000_000_000

func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	t := getNextInt(scanner)
	for t > 0 {
		t--
		func() {
			n := getNextInt(scanner)
			a := getNextInt(scanner)
			w := getNextInt(scanner)
			k := getNextInt(scanner)
			if n == k {
				ww := make([]int, n)
				for i := 0; i < n; i++ {
					ww[i] += w / n
				}
				w %= n
				for i := 0; i < w; i++ {
					ww[i]++
				}
				for i := 1; i < w; i++ {
					a--
				}
				for i := 0; i < n-1; i++ {
					if ww[i] != ww[i+1] && i <= a {
						fmt.Fprintln(writer, -ww[0]*(ww[0]+1)/2+a/n)
						return
					}
				}
				ww[0]++
				fmt.Fprintln(writer, -ww[0]*(ww[0]+1)/2+a/n)
				return
			}
			l := -1
			r := Inf
			for l+1 < r {
				m := (l + r) >> 1
				if (m+1)*(k-1)+m > a {
					r = m
					continue
				}
				l = m
			}
			if l < 0 {
				fmt.Fprintln(writer, ":(")
				return
			}
			fmt.Fprintln(writer, l)
		}()
	}
}
func bf(md int) int {
	l := -1
	r := Inf
	for l+1 < r {
		m := (l + r) >> 1
		if m*(m+1)/2 < md {
			l = m
			continue
		}
		r = m
	}
	return r
}