#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define Pi pair<int,int>
#define IINF 1e9
#define LINF 1e18
#define vi vector<int>
#define mp make_pair
#define pb push_back

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 0, 1,0,-1};
int dy[] = { 1, 0,-1,0};
int dx8[] = { -1,-1,-1,0,0,1,1,1};
int dy8[] = { -1,0,1,-1,1,-1,0,1};

unsigned long long sttoi(std::string str) {
	unsigned long long ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

ull gcd(ull a, ull b) {
	if (b > a)swap(a, b);
	if (b == 0) return a;
	return gcd(b, a%b);
}

int comb(int n, int k) {
	int ans = 1;
	for (int i = 0; i < min(k, n - k); i++) {
		ans *= n - i;
		ans /= i + 1;
	}
	return ans;
}

ll mod_pow(ll n,ll p,ll mod){	
	if (p == 0) return 1 % mod;
	if (p < 2) {
		return n % mod;
	}else {
		ll d = 2, value = (n%mod)*(n%mod)%mod;
		while (d*2 < p) { d *= 2;	value *= value;	value %= mod;}
		value %= mod;
		return ((value%mod) * (mod_pow(n, p - d, mod)%mod)) % mod;
	}
}

void solve() {
	ll h, w, n, k;
	cin >> h >> w >> n >> k;
	if (k > h*w) {
		P("NO");
	}
	else {
		if (((h-1)+(w-1)) % n == k-1) {
			P("YES");
		}
		else {
			P("NO");
		}
	}
}

int main() {
	solve();
	return 0;
}