#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <queue>
#include <map>
using namespace std;
typedef long long LL;

LL a,b,c,d,e,f;

int main(){
	ios::sync_with_stdio(false);
	cin >> a >> b >> c >> d;
	e = (c - 1) / b + 1;
	f = (a - 1) / d + 1;
//	cout << e << ' ' << f << endl;
	cout << (e > f ? "No" : "Yes") << '\n';
	return 0;
}