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) {
		double xf= (p-m)/d;
		int x = (int) (xf);
		int valTillNow = (x+1)*p - (x)*(x+1)*d/2;
		if(valTillNow < s){
		int rest = (s-valTillNow)/m;
		return x+rest+1;
		} else {
			int sum=0;
			int count = 0;
			while(sum<s) {
				sum += (p-count*d);
				count++;
			}
			if(sum<=s) {
			return count;
			} else {
				return count-1;
			}
		}
		
	}

    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();
    }
}