#include <bits/stdc++.h>

#define endl '\n'
#define fi first
#define se second
#define MOD(n,k) ( ( ((n) % (k)) + (k) ) % (k))
#define forn(i,n) for (int i = 0; i < n; i++)
#define forr(i,a,b) for (int i = a; i <= b; i++)
#define all(v) v.begin(), v.end()
#define pb(x) push_back(x)

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

int a, b, c, d;

int main () {
	ios_base::sync_with_stdio(0); cin.tie(0);
	
	cin >> a >> b >> c >> d;

	while (1) {
		if (a <= 0) {
			cout << "No" << endl;
			return 0;
		}

		c -= b;

		if (c <= 0) {
			cout << "Yes" << endl;
			return 0;
		}

		a -= d;
	}

	return 0;
}
