#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()
{
	ll h,w,n,k;
	cin>>h>>w>>n>>k;
	ll p=((h-1)+(w-1)+1)%n;
	if(!p)p=n;
	if(k==p)cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
	return 0;
}