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

#define LL long long

#define FOR(INDEX, START, END) for (LL INDEX = (START); INDEX < (END); ++INDEX)
#define REP(INDEX, COUNT) for (LL INDEX = 0; INDEX < (COUNT); ++INDEX)

int main()
{
	LL A, B, C, D;
	cin >> A >> B >> C >> D;

	for (;;) {
		C -= B;
		if (C <= 0) {
			cout << "Yes" << endl;
			break;
		}

		A -= D;
		if (A <= 0) {
			cout << "No" << endl;
			break;
		}
	}

	return 0;
}
