// returns minimal time needed
static <A> Timed<A> timedForNSeconds(double n, S desc default str(f), IF0<A> f) {
  long start = sysNow(), min = -1, print = sysNow();
  int seconds = 1;
  long count = 0, sum = 0;
  A result = null;
  while (seconds <= n) {
    long time = nanos();
    result = f!;
    ++count;
    time = nanos()-time;
    min = min < 0 ? time : min(min, time);
    sum += time;
    double avg = doubleRatio(sum, count);
    if (sysNow() >= start+seconds*1000) {
      printAndSetConsoleTitleIfMain(
        "avg=" + formatDouble(nanosToMS(avg), 3) + " ms, " +
        "min=" + formatDouble(nanosToMS(min), 3) + " ms: " +
        desc + " (" + seconds + "/" + n + " s, last=" + formatDouble(nanosToMS(time), 3) + " ms, " + n2(count) + "/s)");
      ++seconds;
      count = sum = 0;
    }
  }
  ret Timed<A>(result, nanosToMS(min));
}