#include <bits/stdc++.h>
#define sz(c)       int(c.size())
#define rep(i,a,b)  for (int i=a; i<(b); ++i)
#define per(i,a,b)  for (int i=(b)-1; i>=(a); --i)
#define fore(c,...) for (auto __VA_ARGS__:(c))
using namespace std;
typedef long long ll;



int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	cout<<fixed<<setprecision(10);

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

	while (true) {
		c-=b;
		if (c<=0) {
			cout<<"Yes"<<'\n';
			return 0;
		}
		a-=d;
		if (a<=0) {
			cout<<"No"<<'\n';
			return 0;
		}
	}
}
