#include <iostream>

using namespace std;
using LL = long long;
using ULL = unsigned long long;

int main() {
    int N, M, X, Y;
    cin >> N >> M >> X >> Y;

    int x, y;
    x = --X % M;
    y = --Y % M;
    if ((X / M) & 1) x = M - 1 - x;
    if ((Y / M) & 1) y = M - 1 - y;

    cout << (x == y ? "YES" : "NO") << endl;
}