#include<bits/stdc++.h>
using namespace std;
using ll=long long;
constexpr ll mod=1000000007;

int A,B,C,D;

int main(){
	cin>>A>>B>>C>>D;
	while(true){
		C-=B;
		if(C<=0){
			puts("Yes");
			return 0;
		}
		A-=D;
		if(A<=0){
			puts("No");
			return 0;
		}
	}
}
