#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main()
{
	int a,b,c,d;
	cin>>a>>b>>c>>d;
	
	while(a>=0 && b>=0)
	{
		c-=b;
		if(c<=0)
		{
			cout<<"Yes"<< endl;
			break;
		}
		a-=d;
		if(a<=0)
		{
			cout<<"No"<< endl;
			break;
		}
	}
	
	return 0;
}
