#include<iostream>
#include<algorithm>
#include<functional>
#include<cmath>
#include<string>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<deque>
using namespace std;
#define ll long long
const int mod = 1000000007;
const ll INF = 1000000000000000000;

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