// clang-format off
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
#define rep(i,n) for(ll i=0, i##_len=(n); i<i##_len; ++i)
#define rep1(i,n) for(ll i=1, i##_len=(n); i<=i##_len; ++i)
#define rrep(i,n) for(ll i=n-1; i>=0; --i)
#define rrep1(i,n) for(ll i=n; i>0; --i)
#define all(x) (x).begin(),(x).end()
#define SORT(x) sort(all(x))
#define SORT_DESC(x) sort((x).rbegin(),(x).rend())
#define pb push_back
#define mp make_pair
#define coutl cout<<fixed<<setprecision(10)
#define ANS(ans) cout<<ans<<endl;
const ll LINF = (1LL << 62) - 1;
const int INF = (1 << 30) - 1;
template<class T>bool chmax(T &a, const T &b){if (a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a, const T &b){if (b<a){a=b;return 1;}return 0;}
const string YES = "Yes";
const string NO = "No";
// clang-format on

void solve(long long A, long long B, long long C, long long D) {
  ll t = C / B, a = D / A;
  ANS((t - 1 >= a ? YES : NO));
}

// clang-format off
int main() {
  long long A;
  scanf("%lld",&A);
  long long B;
  scanf("%lld",&B);
  long long C;
  scanf("%lld",&C);
  long long D;
  scanf("%lld",&D);
  solve(A, B, C, D);
  return 0;
}
