#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>

#define ll long long
#define rep(cnt,a,n) for(ll cnt=a;cnt<n+a;cnt++) //aから始めてn回ループ

using namespace std;
int main()
{
    ll a;
    ll b;
    ll c;
    ll d;
    cin >> a;
    cin >> b;
    cin >> c;
    cin >> d;
    while (a > 0 || c > 0) {
        c -= b;
        if (c <= 0) {
            cout << "Yes" << endl;
            return 0;
        }
        a -= d;
        if (a <= 0) {
            cout << "No" << endl;
            return 0;
        }

    }

    return 0;
}