#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
const int inf = 1e9;
const ll INF = 1e18;
const double pi = 3.14159265358979323846;
#define rep(i,n) for(ll i=0;i<n;i++)

int main(){
	int a,b,c,d;cin>>a>>b>>c>>d;
	while(1){
		c-=b;
		if(c<=0){
			cout<<"Yes"<<"\n";
			return 0;
		}
		a-=d;
		if(a<=0){
			cout<<"No"<<"\n";
			return 0;
		}

	}
}