#include<bits/stdc++.h>
using namespace std;
int main()
{
int a ,b,c,d;
cin>>a>>b>>c>>d;
int c1=c/b,c2=a/d;
if(c%b)
    c1++;
if(a%d)
    c2++;

if(c1<=c2)
    cout<<"Yes\n";
else
    cout<<"No\n";



return 0;
}
