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

// #define int long long

signed main()
{
    int i=0, j=0, k=0, ans=0;
    int A,B,C,D;
    cin>>A>>B>>C>>D;

    int ans1, ans2;
    ans1=A/D;
    if(A%D)
        ans1++;
    ans2=C/B;
    if(C%B)
        ans2++;

    if(ans2<=ans1)
        cout<<"Yes"<<endl;
    else
        cout<<"No"<<endl;
    return 0;
}