t: let
  rem = x: y: x - x / y * y;
  days = t / 86400;
  secondsInDay = rem t 86400;
  hours = secondsInDay / 3600;
  minutes = (rem secondsInDay 3600) / 60;

  # Courtesy of https://stackoverflow.com/a/32158604.
  z = days + 719468;
  era = (if z >= 0 then z else z - 146096) / 146097;
  doe = z - era * 146097;
  yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
  y = yoe + era * 400;
  doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
  mp = (5 * doy + 2) / 153;
  d = doy - (153 * mp + 2) / 5 + 1;
  m = mp + (if mp < 10 then 3 else -9);
  y' = y + (if m <= 2 then 1 else 0);

  pad = s: if builtins.stringLength s < 2 then "0" + s else s;
in "${toString y'}-${pad (toString m)}-${pad (toString d)}-${pad (toString hours)}:${pad (toString minutes)}"