diff --git a/lab39.py b/lab39.py
new file mode 100644
index 0000000..7427200
--- /dev/null
+++ b/lab39.py
@@ -0,0 +1,41 @@
+def format_time(hh, mm, ss):
+    return f"{hh:02d}:{mm:02d}:{ss:02d}"
+
+class Timer:
+    def __init__(self, hours, minutes, seconds):
+        self.__hours = hours
+        self.__minutes = minutes
+        self.__seconds = seconds
+
+    def __str__(self):
+        return format_time(self.__hours, self.__minutes, self.__seconds)
+
+    def next_second(self):
+        self.__seconds += 1
+        if self.__seconds > 59:
+            self.__seconds = 0
+            self.__minutes += 1
+        if self.__minutes > 59:
+            self.__minutes = 0
+            self.__hours += 1
+        if self.__hours > 23:
+            self.__hours = 0
+
+    def prev_second(self):
+        self.__seconds -= 1
+        if self.__seconds < 0:
+            self.__seconds = 59
+            self.__minutes -= 1
+        if self.__minutes < 0:
+            self.__minutes = 59
+            self.__hours -= 1
+        if self.__hours < 0:
+            self.__hours = 23
+
+
+timer = Timer(23, 59, 59)
+print(timer)
+timer.next_second()
+print(timer)
+timer.prev_second()
+print(timer)