#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using mii = map<int, int>;
using mll = map<ll, ll>;
using vi = vector<int>;
using vii = vector<vi>;
using vpi = vector<pii>;
using vl = vector<ll>;
using vll = vector<vl>;
using vpl = vector<pll>;
using vs = vector<string>;

int main()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    bool ans = true;
    while(true)
    {
        c -= b;
        if(c <= 0)
        {
            ans = true;
            break;
        }
        a -= d;
        if(a <= 0)
        {
            ans = false;
            break;
        }
    }
    if(ans) cout << "Yes" << endl;
    else cout << "No" << endl;
    return 0;
}
