// きさま！ 見ているなッ！

#include<iostream>
#include<queue>
#include<memory>
#include<map>
#include<set>
#include<unordered_map>
#include<array>
#include<vector>
#include<algorithm>
#include<list>
#include<limits>
#include<stdio.h>
#include<math.h>
#include<string>
#include<thread>

using namespace std;
using ll = long long;
using vec = vector<int>;
using mat = vector<vec>;
using lst = list<ll>;

const ll MOD = 1000000007;


int main()
{
	int A, B, C, D;
	cin >> A >> B >> C >> D;
	while(true)
	{
		C -= B;
		if (C <= 0)
		{
			cout << "Yes" << endl; return 0;
		}
		A -= D;
		if (A <= 0)
		{
			cout << "No" << endl; return 0;
		}
	}

	return 0;
}

