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 g=0;
        int k,c=2;
        k=p-d;
        g=p+k;
        while(k>=m){
            k=k-d;
            g=g+k;
            c++;
        }
        if(g==s){
            return c;
        }
        else{
             while(g<=s){
               g=g+k;
                 if(g<s){
                     c++;
                 }
                 else{
                     continue;
                 }
            
        }
            return c;
        }
        
        
        // Return the number of games you can buy
    }

    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();
    }
}