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

public class Solution {

    
    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 val=0,count=-1;
        while(val<=s){
            val=val+p;
            count++;
            p=p-d;
            if(p<m){
               p=m;
                
        }
     
      
    } System.out.println(count);
}
}