#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define MP make_pair
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define PLI pair<ll, int>
#define PIL pair<int, ll>
#define STR string
#define Fst first
#define Snd second
#define SHN 1e9
#define LSHN 1e18
using namespace std;
int a,b,c,d;
int main()
{
	cin >>a>>b>>c>>d;
	while (a>0 && c>0)
	{
		//cout <<a<<" "<<c<<" ##\n";
		c-=b;
		if (c<=0)
		{
			cout <<"Yes";
			break;
		}
		a-=d;
		if (a<=0)
		{
			cout <<"No";
			break;
		}
	}
	return 0;
} 