#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int x = (a + d - 1) / d;
    int y = (c + b - 1) / b;
    if (x >= y) cout << "Yes" << endl;
    else cout << "No" << endl;
}