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 count = 0;
        int sum = p;
        int previousCost = p;

        while(sum <= s) {
            int i = previousCost - d;
            int currentCost = i <=m ? m : i;
            previousCost = currentCost;
            sum = sum + currentCost;
            count ++;
        }
        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();
    }
}