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


int main()
{

    int a,b,c,d;
    cin>>a>>b>>c>>d;

    int cnt=0;
    while(a>0&&c>0){
        if(cnt%2==0)
            c-=b;
        else
            a-=d;

        cnt++;
    }

    if(a>0)
        cout<<"Yes"<<endl;
    else
        cout<<"No"<<endl;

    return 0;
}   