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

int solve(int n,int m,int xy){
	int ret=xy%(2*m);
	if(ret<=m)return ret;
	else return m*2-ret+1;
}

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;
}