#pragma region template
#include "bits/stdc++.h"
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
const long long MOD = 1e9 + 7, MAX = 1e18, larg = 1e5, INF = -1e9;
long long A, B, C, D, E, F, G, H, I, J, K, L, N, M, O, P, Q, R, S, T, U, V, W, x, y, z;
long long max_value = INF, max_index = -1;
long long min_value = MAX, min_index = -1;
typedef long long ll;
typedef pair<ll, ll> Pa;

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