#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n,m,x,y;
    cin >> n >> m >> x >> y;
    x--;y--;
    x%=(2*m);
    y%=(2*m);
    int cl[2];
    if((x/m)%2==0)cl[0]=x+1;
    else cl[0]=2*m-x;

    if((y/m)%2==0)cl[1]=y+1;
    else cl[1]=2*m-y;

    if(cl[0]==cl[1])cout << "YES";
    else cout << "NO";
    cout << endl;
    return 0;
}