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 numOfGames=1;
        int sum=20;
        while(sum<=s)
        {
            if((p-d)>=m)
            {
                sum=sum+p;
                p=p-d;
            }
            else
            {
                sum=sum+d;
            }
            numOfGames++;
        }
        return numOfGames;
        // 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();
    }
}