#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef unsigned long long int ull;
typedef vector<ll> vi;
typedef pair<ll, ll> pii;
typedef tuple<ll, ll, ll> tii;
typedef vector<pii> vii;

#define pb push_back
#define mp make_pair
#define sq(a) (a)*(a)
#define rep(i,a,b) for (int i = a; i < b; i++)
#define mod 1e9+7
#define PI 3.141592653589793238
#define phi 1.638
#define eps 1e-7

#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);


int gcd(int a, int b)
{
	if (b == 0)
		return a;
	return gcd(b, a % b);
}

int main()
{
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif

	IOS

	ll a, b, c, d;
	cin >> a >> b >> c >> d;
	double t1 = ceil((double)c / b);
	double t2 = ceil((double)a / d);
	if (t1 - t2 > 0)
		cout << "No" << endl;
	else
		cout << "Yes" << endl;

	return 0;
}