#include <bits/stdc++.h>

using namespace std; 
#define REP(i, n) for (int i = 0; i < (n); i++)

typedef long long ll;
int main(int argc, char const *argv[])
{
    cin.tie(0);
   	ios::sync_with_stdio(false);
    ll A, B, C, D; cin >> A >> B >> C >> D;
    string ans = (C/B + (C%B!=0) <= A/D + (A%D!=0)) ? "Yes" : "No";
    cout << ans << endl;
    return 0;
}
