#include <bits/stdc++.h>
#define REP(i,n) for(int i=0;i<(n);++i)
#define ALL(v)   (v).begin(),(v).end()
#define debug(x) cerr<<#x<<": "<<(x)<<endl
#define INF      (int)1e9
#define EPS      (double)1e-9
#define MOD      ((int)1e9+7)
using namespace std;
typedef long long     llong;
typedef vector<int>   vi;
typedef vector<vi >   vvi;
typedef vector<vvi >  vvvi;
typedef pair<int,int> pii;
template<class Type> void line(const Type &a){int cnt=0;for(const auto &elem:a){if(cnt++)cout<<' ';cout<<elem;}cout<<endl;}

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