#include<bits/stdc++.h>
using namespace std;

#define REP(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)
typedef long long ll;
//typedef long long int;
const ll M = 1000000007;
ll A, B, C, D, G, H, N, L, K, P, Q, R, W, X, Y, Z;
string S, T;

signed main(){
	std::cin >> A>>B>>C>>D;
	int t,a;
	t = (C + B - 1) / B;
	a = (A + D - 1) / D;
	if (a<t){
	std::cout << "No" << std::endl;}
	else
	std::cout << "Yes" << std::endl;
}