#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,m,x,y; 
string ans[]={"NO","YES"};
int main(){
	cin>>n>>m>>x>>y;
	x%=(m*2),y%=(m*2);
	cout<<ans[(x==y||(x+y==m*2+1))];
}