#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;

typedef long long ll;
//typedef modint1000000007 mint;
const int MOD = 1000000007;
#define all(x) x.begin(), x.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
const int inf = 1 << 30;
const ll INF = 1LL << 60;
const int dx[8] = {1, 0, -1, 0, -1, -1, 1, 1};
const int dy[8] = {0, 1, 0, -1, -1, 1, -1, 1};
template <class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template <class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

int main(){
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x--, y--;
    x %= 2 * m, y %= m * 2;

    if(x >= m) x = 2 * m - x - 1;
    if(y >= m) y = 2 * m - y - 1;

    if(x == y) cout << "YES" << endl;
    else cout << "NO" << endl;

    return 0;
}