#define _USE_MATH_DEFINES
#include <algorithm>
#include <bitset>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
#include <random>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };
typedef vector<vector<bool> > grid;

ll INF = LLONG_MAX / 3;
ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

ll f(ll x, ll M) {
	x %= (M * 2);
	if (x >= M) return M * 2 - 1 - x;
	return x;
}

int main() {
	ll N, M; cin >> N >> M;
	ll x, y; cin >> x >> y; x--; y--;
	cout << (f(x, M) == f(y, M) ? "YES" : "NO") << endl;
}