#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<cstring>
#include<cstdlib>
#include<string>
#include<numeric>
using namespace std;

#define int long long
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(v) (v).begin(),(v).end()
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}


signed main(){
    int n,m,x,y;
    cin>>n>>m>>x>>y;
    x--;y--;
    x%=2*m;
    y%=2*m;
    if(x>=m)x=2*m-1-x;
    if(y>=m)y=2*m-1-y;
    if(x==y)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}