#include <stdio.h>

int n, m;

int f(int x) {
	int z = x % (2 * m);
	return z < m ? z : (m - 1) - z % m;
}

int main () {
	int x, y;
	scanf("%d%d%d%d", &n, &m, &x, &y);
	
	printf("%s\n", f(x-1) == f(y-1) ? "YES" : "NO" );
	
	return 0;
}