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;
        int counter = 0;
        while(true){
            sum += p;
            
            if(sum > s)
                break;
            
            counter ++;
            
            if(p > m)
                p -= d;
            if(p <= m)
                p = m;
        }
        
        return counter;
    }

    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();
    }
}