#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N,M,X,Y; cin >> N >> M >> X >> Y;
    X--; Y--;
    if(X / M % 2 == Y / M % 2) {
        cout << (X % M == Y % M ? "YES" : "NO") << "\n";
    } else {
        cout << (X % M == M - 1 - Y % M ? "YES" : "NO") << "\n";
    }
}