#include <bits/stdc++.h> #define syosu(x) fixed<<setprecision(x) using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair<int,int> P; typedef pair<double,double> pdd; typedef pair<ll,ll> pll; typedef vector<int> vi; typedef vector<vi> vvi; typedef vector<long double> vd; typedef vector<vd> vvd; typedef vector<ll> vl; typedef vector<vl> vvl; typedef vector<string> vs; typedef vector<P> vp; typedef vector<vp> vvp; typedef vector<pll> vpll; typedef pair<int,P> pip; typedef vector<pip> vip; const int inf=1<<30; const ll INF=1ll<<60; const double pi=acos(-1); const double eps=1e-6; const ll mod=1e9+7; const int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0}; ll n,m,x,y; ll f(ll A){ A--; ll t=A/m; if(t%2==0) return A%m; return m-A%m-1; } int main(){ cin>>n>>m>>x>>y; cout<<(f(x)==f(y)?"YES":"NO")<<endl; }