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

int solve(int n,int m,int xy){
	int a=(xy+m-1)/m,b=xy%m;
	int ret;
	if(a&1){
		if(b==0)ret=m;
		else ret=b;
	}
	else{
		ret=m+1-b;
	}
	return ret;
}

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	int n,m,x,y; cin>>n>>m>>x>>y;
	cout<<(solve(n,m,x)==solve(n,m,y)?"YES"s:"NO"s)<<"\n"s;
}