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