void main(String... args) {
    int size = 50_000_000;
    if (args.length > 0) size = Integer.parseInt(args[0]);
    LocalDate[] arr = makeArray(size);
    for (int i = 1; i <= 5; i++) {
        double t = time(() -> sumYears(arr));
        IO.println("Attempt " + i + ": " + t);
    }
}

/// Expensive task to be timed
long sumYears(LocalDate[] dates) {
    long result = 0;
    for (var d : dates) result += d.getYear();
    return result;
}

/// Make an array of LocalDates, unpredictably ordered
LocalDate[] makeArray(int size) {
    HashSet<LocalDate> set = new HashSet<>();
    for (int i = 0; i < size; i++) set.add(LocalDate.ofEpochDay(i));
    return set.toArray(new LocalDate[0]);
}

/// Run a task and report the elapsed wall-clock time in ms
double time(Runnable r) {
    var start = Instant.now();
    r.run();
    var end = Instant.now();
    return Duration.between(start, end).toNanos() / 1_000_000.0;
}