#include <bits/stdc++.h>
using namespace std;
#define mod 1e9+7
typedef long long ll; 
typedef vector<long long> vi; 
typedef pair<int, int> ii; 
typedef vector<ii> vii; 
typedef set<int> si; 
typedef map<string, int> msi; 

int main(){
  ios_base::sync_with_stdio(false); 
    cin.tie(NULL);
    ll a,b,c,d,x=0;
    cin>>a>>b>>c>>d;
   while(1){
   c=c-b;
     if(c<=0){
       x=1;break;
   }
     a=a-d;
     if(a<=0){
     x=2;break;
     }
   }
  if(x==1) cout<<"yes";
  else if(x==2) cout<<"no";
  return 0;}