#include "bits/stdc++.h"
#include "math.h"
 
using namespace std;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<int> vin;
typedef vector<pair<ll,ll> > vp;
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
const int MOD = 1000000007;
const int MAX = 510000;

int main(){
  ll a,b,c,d;cin>>a>>b>>c>>d;
  ll x=a/d,y=c/b;
  if(a%d!=0){x++;}
  if(c%b!=0){y++;}
  if(y>x){cout<<"No"<<endl;}
  else{cout<<"Yes"<<endl;}
}

