#include <cstdio>
#include <cstring>
#include <cmath>
#include <cassert>
#include <random>
#include <vector>
#include <algorithm>
#include <array>
#include <functional>
#include <utility>
#include <regex>
#include <tuple>
#include <map>

using namespace std;

int main(){
	int64_t n,m,x,y;
	-scanf("%ld%ld%ld%ld",&n,&m,&x,&y);
	x--;y--;
	x=x%(m*2);
	if(x>=m){
		x=m*2-x-1;
	}
	y=y%(m*2);
	if(y>=m){
		y=m*2-y-1;
	}
	puts(x==y?"YES":"NO");
	return 0;
}