#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
  int n,m,x,y;
  cin>>n>>m;
  cin>>x>>y;
  int a,b,c,d;
  a=(x-1)/m;
  b=x%m;
  c=(y-1)/m;
  d=y%m;
  int e,f;
  if(a%2==1){
    if(b==0){
      e=m;
    } else {
      e=b;
    }
  } else {
    if(b==0){
      e=1;
    } else {
      e=m-b+1;
    }
  }
  if(c%2==1){
    if(d==0){
      f=m;
    } else {
      f=d;
    }
  } else {
    if(d==0){
      f=1;
    } else {
      f=m-d+1;
    }
  }
  if(e==f){
    cout<<"YES"<<endl;
  } else {
    cout<<"NO"<<endl;
  }
  return 0;
}