#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)
#define all(a) (a).begin(),(a).end()

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    ll N, M, X, Y;
    cin >> N >> M >> X >> Y;
    
    X--, Y--;
    
    X %= M * 2;
    Y %= M * 2;
    
    if (X >= M) X = M - 1 - X % M;
    if (Y >= M) Y = M - 1 - Y % M;
    
    cout << (X == Y ? "YES" : "NO") << '\n';
}