#include <stdio.h>

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