import java.util.Scanner; public class Yukicoder396 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); long N = sc.nextLong(); long M = sc.nextLong(); long X = sc.nextLong(); long Y = sc.nextLong(); boolean flip = false; long buf = X; while (buf > 0) { buf -= M * 2; } buf += M * 2; if (buf > M) { buf = M * 2 - buf + 1; } long add1 = (M - buf) * 2 + 1; long add2 = M * 2 - add1; while (buf < N) { if (buf == Y) { System.out.println("YES"); return; } if (!flip) { buf += add1; flip = !flip; } else { buf += add2; flip = !flip; } } System.out.println("NO"); } }