#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <functional>
#include <array>
#include <map>
using namespace std;

#define Getsign(n) ((n > 0) - (n < 0))

typedef vector<int> Ivec;
typedef pair<int, int> Pos;

int main() {
	int n, m, x, y, a,b;
	scanf("%d %d %d %d", &n, &m, &x, &y);
	x %= 2 * m;
	y %= 2 * m;
	if (x == 0) x = m * 2;
	if (y == 0) y = m * 2;
	if ((x - m) >= 1) {
		a = m-(x-m)+1;
	}
	else a = x;

	if ((y - m) >= 1) {
		b = m - (y-m)+1;
	}
	else b = y;
	printf("%s\n", a == b ? "YES" : "NO");
	return 0;
}