#include <iostream>
using namespace std;
int main(){
  int n,m,x,y;cin>>n>>m>>x>>y;
  int xc = (((x-1)%(m*2) < m) ? (x-1)%m : m-((x-1)%m-1));
  int yc = (((y-1)%(m*2) < m) ? (y-1)%m : m-((y-1)%m-1));
  if(xc == yc)cout << "YES" << endl;
  else cout << "NO" << endl;
}