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) {
        // Return the number of games you can buy
        if (s < p) return 0;
        int l = (p - m) / d;
        int l1 = l + 1;
        int sum = (p + (p - l * d)) * l1 / 2;
        if (s >= sum) {
            int more = (s - sum) / m;
            return l1 + more;
        } else {
            int left = 1;
            int right = l1 - 1;
            while (left < right - 1) {
                int mid = left + (right - left) / 2;
                int cutoff = (p + (p - (mid - 1) * d)) * mid / 2;
                if (cutoff == s) {
                    return mid;
                } else if (cutoff > s) {
                    right = mid - 1;
                } else {
                    left = mid;
                }
            }
            int cutoff = (p + (p - (right - 1) * d)) * right / 2;
            if (cutoff <= s) {
                return right;
            }
            return left;
        }
    }

    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();
    }
}