import java.util.Locale;
import java.util.Scanner;

public class HalloweenSale {

    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            in.useLocale(Locale.ENGLISH);
            int p = in.nextInt();
            int d = in.nextInt();
            int m = in.nextInt();
            int s = in.nextInt();

            int count = 0;
            int currentPrice = p;
            while (s >= currentPrice) {
                s -= currentPrice;
                currentPrice -= d;
                currentPrice = Math.max(currentPrice, m);
                count++;
            }
            System.out.println(count);

        }
    }


}