#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
using VVI = vector<VI>;
using VVL = vector<VL>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define rep3(i, s, n, d) for (int i = (s); i < (int)(n); i += (d))
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()

const int mod = 1e9 + 7, mod2 = 998244353, mod3 = 1e9 + 9;
const ll inf = 1e18;

const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T>
void show1dvec(const vector<T> &v)
{
    if (v.size() == 0)
        return;
    int n = v.size() - 1;
    rep(i, n) cout << v[i] << wsp;
    cout << v[n] << rt;

    return;
}

template <typename T>
void show2dvec(const vector<vector<T>> &v)
{
    int n = v.size();
    rep(i, n) show1dvec(v[i]);
}

template <typename T, typename S>
void show1dpair(const vector<pair<T, S>> &v)
{
    int n = v.size();
    rep(i, n) cout << v[i].first << wsp << v[i].second << rt;
    return;
}

template <typename T, typename S>
void pairzip(const vector<pair<T, S>> &v, vector<T> &t, vector<T> &s)
{
    int n = v.size();
    rep(i, n)
    {
        t.push_back(v[i].first);
        s.push_back(v[i].second);
    }
    return;
}

template <typename T>
void maxvec(vector<T> &v)
{
    T s = v[0];
    int n = v.size();
    rep(i, n - 1)
    {
        if (s > v[i + 1])
        {
            v[i + 1] = s;
        }
        s = v[i + 1];
    }
}

template <typename T, typename S>
bool myfind(T t, S s)
{
    return find(t.cbegin(), t.cend(), s) != t.cend();
}

bool check(int y, int x, int h, int w)
{
    return 0 <= y && y < h && 0 <= x && x < w;
}

template <typename T>
vector<T> cumsum(const vector<T> &v)
{
    T s = 0;
    vector<T> ret = {0};

    rep(i, v.size())
    {
        s += v[i];
        ret.push_back(s);
    }
    return ret;
}

bool iskadomatsu(int a, int b, int c)
{
    return (a != b && b != c && c != a) && ((a > b && b < c) || (a < b && b > c));
}

VS split(string s, char c)
{
    VS ret;
    string part;
    s += c;
    rep(i, s.length())
    {
        if (s[i] == c)
        {
            ret.emplace_back(part);
            part = "";
        }
        else if (s[i] != c)
        {
            part += s[i];
        }
    }
    return ret;
}

string removezero(string &s)
{
    string ret;
    for (auto z : s)
        if (z != '0')
            ret += z;
    return ret;
}

ll sumdigit(ll x)
{
    ll ans{0};
    while (x > 0)
    {
        ans += x % 10;
        x /= 10;
    }
    return ans;
}

ll pow_mod(int p, int q, int mod)
{
    ll ret = 1, r = p;
    while (q)
    {
        if (q % 2)
            ret *= r, ret %= mod;
        r = (r * r) % mod, q /= 2;
    }
    return ret % mod;
}

ll comb(int a, int b, const VL &frac_list, const VL &frac_inv_list)
{
    ll ret = frac_list[a];
    ret *= frac_inv_list[b];
    ret %= mod;
    ret *= frac_inv_list[a - b];
    ret %= mod;
    return ret;
}

void shave(vector<int> &v, int n)
{
    vector<int> x, y;
    int n_sq = sqrt(n) + 1;
    for (int i = 3; i < n + 1; i += 2)
    {
        x.emplace_back(i);
    }
    for (int i = 3; i < n_sq; i += 2)
    {
        for (auto itr = x.begin(); itr != x.end(); itr++)
        {
            if (*itr == i || *itr % i != 0)
                y.emplace_back(*itr);
        }
        x.clear();
        x = y;
        y.clear();
    }
    if (n >= 2)
        x.insert(x.begin(), 2);

    for (auto itr = x.begin(); itr != x.end(); itr++)
    {
        v.emplace_back(*itr);
    }
}



int main()
{

    cin.tie(0);
    ios::sync_with_stdio(false);

#ifdef DEBUG
    cout << "DEBUG MODE" << endl;
    ifstream in("input.txt"); //for debug
    cin.rdbuf(in.rdbuf());    //for debug
#endif
    const int inf = 1e7;

    int a, b, c, d;
    cin >> a >> b >> c >> d;

    // cout << a << wsp << c << rt;
    int status{0};
    while (!status)
    {
        c -= b;
        // cout << a << wsp << c << rt;
        if (c <= 0)
        {
            status = 1;
            break;
        }
        
        a -= d;
        // cout << a << wsp << c << rt;
        
        if (a <= 0)
        {
            status = 2;
            break;
        }
        
    }
    cout << (status == 1 ? "Yes" : "No") << rt;
    // show1dvec(prime_list);
    // show1dvec(prime_square_list);

    return 0;
}


Measured memory_bytes: 3680