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

int main(){
    int N, M, X, Y;
    cin >> N >> M;
    cin >> X >> Y;
    int gx = (X-1)/M;
    int gy = (Y-1)/M;
    int cx,cy;
    gx%2?cx=(gx+1)*M-X+1:cx=X-gx*M;
    gy%2?cy=(gy+1)*M-Y+1:cy=Y-gy*M;
    cout << (cx==cy?"YES":"NO") << endl;
    return 0;
}