#include<iostream>
using namespace std;

int main(){
	int A, B, C, D;
	cin >> A >> B >> C >> D;
	
	for(int i=0; i<100; i++){
		C -= B;
		if(C<=0){
			cout << "Yes" << endl;
			return 0;
		}
		A -= D;
		if(A<=0){
			cout << "No" << endl;
			return 0;
		}
	}
	
	return 0;
}
