#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
#include<vector>
#include<math.h>
#include<iomanip>
#include<stack>
#include<queue>
#include<set>
#include<map>

using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int , int>;

//const ll mod = 1000000007;
const ll mod = 998244353;
const ld pi = 3.14159265358979;

int main() {
	//ios::sync_with_stdio(false);
	//cin.tie(0);
	//cout << fixed << setprecision(15);
	int h , w;
	ll n , k;
	cin >> h >> w >> n >> k;
	ll hw = (ll)h * w - 1;
	ll m = hw % n + 1;
	cout << (m == k ? "YES" : "NO") << endl;

	return 0;
}