import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt(), M = sc.nextInt(), P = sc.nextInt(), Q = sc.nextInt(), i;
        sc.close();
        for (i = 0; N > 0; ++i) {
            if (i % 12 + 1 >= P && i % 12 + 1 < P + Q) N -= 2 * M;
            else N -= M;
        }
        System.out.print(i);
    }
}