#include <bits/stdc++.h>

using namespace std;

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

    int i=0;

    while(true){
        if(c-b*i<=0){
            cout<<"Yes"<<endl;
            return 0;
        }
        if(a-d*i<=0){
            cout<<"No"<<endl;
            return 0;
        }
        i++;
    }
}