#include <stdio.h>

int main(){
	int N, M, X, Y, a, b, HanakoRank, TarouRank;
	scanf("%d %d",&N,&M);
	scanf("%d %d",&X,&Y);
	
	if(a > 2*M){
		a = X % 2*M;
	}
	
	if(b > 2*M){
		b = Y % 2*M;
	}
	
	if(a > M){
		HanakoRank = 2*M - a + 1;
	}else{
		HanakoRank = a;
	}
	if(b > M){
		TarouRank = 2*M - b + 1;
	}else{
		TarouRank = b;
	}
	
	if(HanakoRank == TarouRank){
		printf("YES");
	}else{
		printf("NO");
	}
	
	  
	return 0;
}