#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repp(i, n) rep(i, 0, n)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
using namespace std;
typedef pair<int, int> P;

signed main(){
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x--; y--;
    int a = x / m, b = y / m;
    if(a % 2 == b % 2) cout << (x % m == y % m ? "YES" : "NO") << endl;
    else cout << (x % m + y % m == m - 1 ? "YES" : "NO") << endl;
}