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

int main()
{
    int a,b,c,d;
    cin>>a>>b>>c>>d;

    while(a>0 && c>0)
    {
        c = c-b;
         a = a-d;
    }
    if(c<=0)
    {
        cout<<"Yes"<<endl;
    }
    else
    cout<<"No"<<endl;

    return 0;

}
