#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <math.h>
#include <string.h>
#include <map>
#include <numeric>
#include <random>
#include <queue>
#include <deque>
#include <tuple>
#include <iomanip>
#include <iterator>
#include <functional>

using namespace std;
typedef long long ll;

const int INF = (1 << 30) - 1;
const ll INFLL= (1LL << 61) - 1;
const int MOD = 1000000007;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  ll N,M,X,Y;
  cin>>N>>M>>X>>Y;
  X--;Y--;
  bool ans=false;
  if(X/M%2==Y/M%2){
    if(X%M==Y%M)ans=true;
  }else{
    if((X+Y)%M==M-1)ans=true;
  }
  if(ans)cout<<"YES"<<endl;
  else cout<<"NO"<<endl;
}