import java.io.*;
import java.util.Scanner;


public class Main_yukicoder740 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int n = sc.nextInt();
		int m = sc.nextInt();
		int p = sc.nextInt();
		int q = sc.nextInt();

		int rem = n;
		for (int i = 1; i <= n; i++) {
			int mo = i % 12;
			if (mo == 0) {
				mo = 12;
			}
			
			if (mo >= p && mo <= p + q - 1) {
				rem -= 2 * m;
			} else {
				rem -= m;
			}

//			pr.println(rem);
			if (rem <= 0) {
				pr.println(i);
				break;
			}
		}
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);
			
		solve();
			
		pr.close();
		sc.close();
	}

	static class Printer extends PrintWriter {
		Printer(OutputStream out) {
			super(out);
		}
	}
}