#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<bitset>
#include<utility>
#include<sstream>
#include<cctype>
#include<cmath>
#include<algorithm>
using namespace std;

#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define repp(i,n) for(int (i)=1;(i)<=(n);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define clr(a) memset((a), 0 ,sizeof(a))


typedef pair<int,int> P;
typedef vector<pair<int,int> > pii;
typedef map<string,int> mi;


int F(int x,int m){
	x=x%(2*m);
	if(m<=x) x=m-1-(x%m);
	return x;
}

int main(){
	int n,m,x,y;
	cin >> n >> m >> x >> y;
	x--,y--;
	
	cout << (F(x,m)==F(y,m)?"YES":"NO") << endl;
	return 0;
}