#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>
#include <string>
#include <iomanip>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <complex>
#include <ctime>


using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef int itn;
const ll LINF = 1e18;
const int INF = 1e9;

//マクロ定義
#define vvint(vec,n,m,l) vector<vector<int>> vec(n, vector<int>(m,l));	// lで初期化
#define vvll(vec,n,m,l) vector<vector<ll>> vec(n,vector<ll>(m,l));
#define vint vector<int>
#define pint pair<int,int>
#define rep(i,a) for(int i=0;i<(a);i++)
#define all(x) (x).begin(),(x).end()
#define debug system("pause")				//デバッグ用
#define ret return 0

template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

using Graph = vector<vector<ll>>;

#define ketasitei setprecision(15) //15桁表示

const ll MOD = 1000000007;
const double PI = 3.1415926535897932;


int main(void)

{
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << ketasitei;

	int a, b, c, d;
	cin >> a >> b >> c >> d;

	for (int i = 0; i <= 100; i++)
	{
		c -= b;
		if (c <= 0)
		{
			cout << "Yes" << endl;
			ret;
		}
		a -= d;
		if (a <= 0)
		{
			cout << "No" << endl;
			ret;
		}
	}

	return 0;
}