import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static int howManyGames(int p, int d, int m, int s) {
        int decrease = (p - m) / d;
        int count = 0;
        int tempSum = (p + p - decrease * d) * (decrease + 1) / 2;
        if (tempSum  <= s) {
            count = decrease + 1 + (s - tempSum) / m ;
        } else {
            int n = 0;
            while (s >= 0) {
                s -= p - n * d;
                n++;
            }
            return n - 1;
        }
        return count;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int p = in.nextInt();
        int d = in.nextInt();
        int m = in.nextInt();
        int s = in.nextInt();
        int answer = howManyGames(p, d, m, s);
        System.out.println(answer);
        in.close();
    }
}