// returns minimal time needed
static long benchForNSeconds(S desc, Runnable r, int n) {
  long start = sysNow(), min = -1, print = sysNow();
  int seconds = 1;
  long count = 0;
  while (seconds <= n) {
    long time = sysNow();
    r.run();
    ++count;
    long now = sysNow();
    time = now-time;
    min = min < 0 ? time : min(min, time);
    if (now >= start+seconds*1000) {
      printAndSetConsoleTitle(min + " ms: " + desc + " (" + seconds + "/" + n + " s, last=" + time + " ms, n=" + count + ")");
      ++seconds;
    }
  }
  ret min;
}