#include <iostream>
#include <stdio.h>

using namespace std;

int f(int m,int x){
	int a1=(x-1)%(m);
	int a2=(x-1)/m;
	if(a2%2==0){
		return a1+1;
	}else{
		return m-a1;
	}
}

int main() {
	// your code goes here
	int n,m,x,y;
	scanf("%d %d %d %d",&n,&m,&x,&y);
	printf("%s\n",f(m,x)==f(m,y)?"YES":"NO");
	
	
	return 0;
}