import java.util.Scanner;
public class Main {
		static int INF = 2 << 27;
		public static void main(String[] args) {
			Scanner sc = new Scanner(System.in);
			int N = sc.nextInt();
			int M = sc.nextInt();
			int X = sc.nextInt();
			int Y = sc.nextInt();
			
			int now = 1;
			int ansX = -1;
			int ansY = -1;
			while(true) {
				if(now > N || (ansX != -1 && ansY != -1)) break;
				if(now + M > X && now <= X) {
					ansX = X - now + 1;
				}
				if(now + M > Y && now <= Y) {
					ansY = Y - now + 1;
				}
				now += M;
				if(now + M > X && now <= X) {
					ansX = now + M - X;
				}
				if(now + M > Y && now <= Y) {
					ansY = now + M - Y;
				}
				now += M;
			}
			if(ansX == ansY) System.out.println("YES");
			else System.out.println("NO");
		}

}