{ Функция проверки, високосный ли год}
function bsYear(n: Word): Boolean;
  begin
    bsYear := ((n mod 4) = 0) and
      not (((n mod 100) = 0) and ((n mod 400) <> 0))
  end;

const
  monthes: array[1 .. 12] of integer =
    (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
  month_name: array[1 .. 12] of string[3] =
    ('jan', 'feb', 'mar', 'apr', 'may', 'jun',
     'jul', 'aug', 'sep', 'oct', 'nov', 'dec');

type
  TData =
    record
      day: 1 .. 31;
      month: 1 .. 12;
      year: word;
    end;

var
  current: TData;
  from_start_year: longint;
  to_sub: integer;

  m_ix: integer;
begin
  { Ввод даты }
  with current do
    begin
      repeat write('месяц: '); readln(month) until month <= 12;
      repeat write('день: '); readln(day); until day <= monthes[month];
      write('год: '); readln(year)
    end;

  write('сколько дней отнять (до 256): '); readln(to_sub);

  from_start_year := 0;
  for m_ix := 1 to pred(current.month) do
    begin
      inc(from_start_year, monthes[m_ix]);
      if (m_ix = 2) and bsYear(current.year) then
        inc(from_start_year);
    end;
  inc(from_start_year, current.day);
  { Сейчас в переменной from_start_year хранится
    число дней от начала года до введенной даты... }

  dec(from_start_year, to_sub);
  if from_start_year < 0 then
    begin
      dec(current.year);
      inc( from_start_year, 365 + byte(bsYear(current.year)) )
    end;

  m_ix := 1;
  while from_start_year > monthes[m_ix] do
    begin
      dec(from_start_year, monthes[m_ix]);
      if (m_ix = 2) and bsYear(current.year) then
        dec(from_start_year);
      inc(m_ix)
    end;
  current.month := m_ix;
  current.day := from_start_year;

  with current do
    writeln( day, ':', month_name[month], ':', year);

end.