#include <bits/stdc++.h>

using namespace std;

int main(){
    int a , b, c, d;
    cin>>a>>b>>c>>d;
    int flag = 0;
    // cout<<"A "<<a << " C "<<c <<endl;
    while(a>0 && c > 0){
        if(flag == 0){
            c = c-b;
            flag = 1;
        }
        else{
            flag = 0;
            a = a-d;
        }
    }
    // cout<<"A "<<a << " C "<<c <<endl;
    if(a <= 0)cout<<"No"<<endl;
    else cout<<"Yes"<<endl;
}