package net.ipipip0129.yukicoder.no740;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int leaf_num = Integer.parseInt(scan.next());
        int leaf_drop_num = Integer.parseInt(scan.next());
        int begin_wind = Integer.parseInt(scan.next());
        int con_wind = Integer.parseInt(scan.next());

        int month_cnt = 0;
        int month = 1;
        int str_wind = 0;

        while (0 < leaf_num) {
            if (begin_wind == month) str_wind = con_wind;

            if (0 < str_wind) leaf_num -= leaf_drop_num * 2;
            else leaf_num -= leaf_drop_num;

            month_cnt += 1;
            month += 1;
            if (0 < str_wind) str_wind -= 1;
            if (month == 13) month = 1;
        }

        scan.close();
        System.out.println(month_cnt);
    }
}