import java.util.*;

public class Main {
    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();
        if( cl(X,M)==cl(Y,M) ){
            System.out.println("YES");
        }else{
            System.out.println("NO");
        }
    }

    static int cl(int a,int b){
        a = (a-1)%(2*b)+1;
        int z=(a-1)/b;
        if(z==0){
            return a;
        }else{
            return 2*b+1-a;
        }
    }
}