#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define vi vector<int>
#define vll vector<ll>
#define pll pair<ll,ll>
#define pii pair<int,int>
#define pb  push_back
#define ppb pop_back
#define mp  make_pair
int main(){
	// #ifndef ONLINE_JUDGE
	// freopen("input.txt", "r", stdin);
	// freopen("output.txt", "w", stdout);
	// #endif
	ios_base::sync_with_stdio(false); 
	cin.tie(NULL);
	ll A,B,C,D;
	cin>>A>>B>>C>>D;
	ll c1=(C+B-1)/B;
	ll c2=(A+D-1)/D;
	if(c1>c2){
		cout<<"No\n";
	}
	else{
		cout<<"Yes\n";
	}
}