#include<iostream>
using namespace std;
int main()
{
	int a,b,c,d;
	cin>>a>>b>>c>>d;
	int m,n;
	if (b==0) cout<<"No";
	else if (d==0) cout<<"Yes";
	else{
	
	if (c%b==0) m=c/b;else m=c/b+1;
	if (a%d==0) n=a/d;else n=a/d+1;
	if (m<=n) cout<<"Yes";else cout<<"No";
	}
}