#include<iostream>
//#include<vector>

int main(){
	int a, b, c, d, ta, ao;
	std::cin>>a>>b>>c>>d;

	if (c%b != 0) {
		ta = c / b + 1;
	}
	else {
		ta = c / b;
	}

	if (a%d != 0) {
		ao = a / d + 1;
	}
	else {
		ao = a / d;
	}

	if (ta <= ao) {
		std::cout << "Yes" << std::endl;
	}
	else {
		std::cout << "No" << std::endl;
	}


	
	return 0;
}