#include<algorithm>
#include<cmath>
#include<cstdio>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<numeric>
#include<queue>
#include<set>
#include<string>
#include<utility>
#include<vector>

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll MOD = 1000000007;
#define rep(i,n) for(int i=0;i<n;i++)
#define repl(i,s,e) for(int i=s;i<e;i++)
#define reple(i,s,e) for(int i=s;i<=e;i++)
#define revrep(i,n) for(int i=n-1;i>=0;i--)
#define all(x) (x).begin(),(x).end()

int main()
{	
	ll H, W, N, K;
	cin >> H >> W >> N >> K;

	if ((H + W - 1) % N == K)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;

	return 0;
}