#include<bits/stdc++.h>
using namespace std;
#define ll long long int
int main()
{
	ll i,j,k,m,n,t;
	ll a,b,c,d;
	cin>>a>>b>>c>>d;
	while(true)
	{
		c-=b;
		if(c<=0)
		{
			cout<<"Yes";
			break;
		}
		a-=d;
		if(a<=0)
		{
			cout<<"No";
			break;
		}
	}
}