#include <iostream>
#include "assert.h"

using namespace std;

int main(){
	long long N,M,X,Y;
	cin >> N >> M >> X >> Y;
	
	assert(2<=N && N<=1000000000);
	assert(1<=M && M<=1000000000);
	assert(1<=X && X<=N);
	assert(1<=Y && Y<=N);
	assert(X!=Y);
	

	auto get_class = [&](long long Z) -> long long{
		Z--;
		if( (Z/M)%2 == 0 ) return Z%M + 1;
		else return M - Z%M;
	};
	
	cout << ( get_class(X)==get_class(Y) ? "YES" : "NO" ) << endl;
	return 0;
}