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 sum=0,count=0;
        while(sum<s){
            sum=sum+p;
            if(sum>s)
                break;
            count++;
            p=p-d;
            if(p<m){
                p=m;
            }
        }
        if(count==-1)
            return 0;
        return count;
    }

    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();
    }
}