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) {
        if(p>s){
            return 0;
        }
        if(p==s)
            return 1;
        int n = (p-m)/d;
        n += 1;
        int s1 = (2*p)-(n-1)*d;
        s1 = (s1*n)/2;
        int a1 = s; int b1 = 0; int count=0; int t=p;
        if(s1>s){
            while(b1+t<=a1){
                ++count;
                b1 += t;
                t -= d;
            }
            return count;
        }
        else{            
            int rs = s-s1;
            int f1 = rs/m;
            n+=f1;
            return n;    
        }
    }

    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();
    }
}