#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-=B;
    if(C<=0){
        cout<<"Yes"<<endl;
        return 0;
    }
    A-=D;
    if(A<=0){
        cout<<"No"<<endl;
        return 0;
}
}
}