#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>

using namespace std;


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

    for (int i = 1;;i++)
    {
        c -= b;
        if (c <= 0)
        {
            cout << "Yes" << endl;
            break;
        }
        a -= d;
        if (a <= 0)
        {
            cout << "No" << endl;
            break;
        }
    }
    
    return 0;
}
