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

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;

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

	ll mx_num = max(H, W) - 1 + min(H, W);
	if (mx_num % N == K || (N == K && mx_num % K == 0))
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
  return 0;
}