#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define P pair<int,int>
using ll=int64_t;
using namespace std;
#define ketasuu(n) fixed<<setprecision(n)
#define btoe(p) p.begin(),p.end()
#define etob(p) p.rbegin(),p.rend()




int main(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    int x=(a+d-1)/d, y=(b+c-1)/b;
    if(x>=y) cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
}