import java.util.*;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int p = sc.nextInt();
		int q = sc.nextInt();
		int a = 0;
		int mo = 1;
		while(n > 0){
			a++;
			if(mo >= p && mo <= p + q - 1){
				n -= 2*m;
			}else{
				n -=m;
			}
			mo++;
			if(mo == 13){
				mo = 1;
			}
		}
		System.out.print(a);
	}
}