#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    int f=1;
    while(a>0&&c>0){
        if(f)c-=b;
        else a-=d;
        f^=1;
    }
    if(a<=0){
        cout<<"No"<<endl;
    }else{
        cout<<"Yes"<<endl;
    }
}
