#include<bits/stdc++.h>
#define ll long long
#define pll pair<ll, ll>
using namespace std;
const ll maxn = 1e6 + 7;
const ll mod = 1e9 + 7;
ll a[maxn], q, t, n, m, k, ans;
priority_queue<ll> pr;
string s, ss, str;
void sol()
{
    ll a, b, c, d;
    cin >> a >> b >> c >> d;
    while(a > 0 && c > 0)
    {
        c -= b;
        if(c <= 0)
        {
            cout << "Yes";
            return;
        }
        a -= d;
        if(a <= 0)
        {
            cout << "No";
            return;
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    sol();
}
