#include<stdio.h>
int main()
{
	int n, m, x, y;
	scanf("%d %d %d %d", &n, &m, &x, &y);
	x--;
	y--;
	x %= 2 * m;
	y %= 2 * m;
	if (x >= m)
		x = 2 * m - x - 1;
	if (y >= m)
		y = 2 * m - y - 1;
	if (x == y)
		printf("YES\n");
	else
		printf("NO\n");
	return 0;
}