#include<bits/stdc++.h>
#define int long long
#define fr first
#define sc second
using namespace std;
int const N=1e6+5;
typedef pair<int,int> pii;
int n,m,sum,cnt,t,ans,x,y;
signed main()
{
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
    cin>>n>>m>>x>>y;
    int nx=x%(m*2);
    int ny=y%(m*2);
    if(nx==ny||nx+ny==2*m+1)   cout<<"YES";
    else cout<<"NO";
	return 0;
}