#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
#define pb push_back
#define mp make_pair
#define fi first
#define se second

int main()
{
	int n,m,a,b,H,T;
	cin>>n>>m>>a>>b;
	int p=a/n,q=a%n;
	int pp=b/n,qq=b%n;
	if(q)
	{
		if(p%2)H=m-p;
		else H=p;
	}
	else
	{
		if(p%2)H=m+1;
		else H=1;
	}
	if(qq)
	{
		if(pp%2)T=m-pp+1;
		else T=pp;
	}
	else
	{
		if(pp%2)T=m;
		else T=1;
	}
	if(H==T)cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
	return 0;
}