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

int main()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;

    int takahashiAttackCount = (c + b - 1) / b;
    int aokiAttackCount = (a + d - 1) / d;

    cout << (takahashiAttackCount <= aokiAttackCount ? "Yes" : "No") << endl;
}