#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cmath>
#include <stack>
#include <queue>
#include <cctype>
#include <stdio.h>
#include <map>
#include <string.h>
#include <utility>

typedef long long ll;


using namespace std;

int main() {

	long  n=0 ,m=0;
	cin>>n>>m;
	int x=0, y=0;
	cin>>x>>y;

	int miss_x=0;
	if(((x-1)/m) %2 ==0){
		miss_x = (x-1)%m;
	}else {
		int tmp = (x-1)%m;

		miss_x = m-1-tmp;
	}

	int mr_y=0;
	if(((y-1)/m) %2 ==0){
		mr_y = (y-1)%m;
	}else {
		int tmp = (y-1)%m;

		mr_y = m-1-tmp;
	}

	if(mr_y == miss_x){
		cout<<"YES"<<endl;
	}else {
		cout<<"NO"<<endl;
	}



	return 0;
}