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