import java.util.*; import java.io.*; import java.math.*; public class No740 { 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(), mo = 1, c = 0; while(n > 0) { c++; n = n - m; if(p <= mo && mo <= p + q - 1) n = n - m; mo = mo < 12? mo + 1 : 1; } System.out.println(c); } }