diff --git a/src/main.py b/src/main.py
index f85701c..4f1bded 100644
--- a/src/main.py
+++ b/src/main.py
@@ -209,25 +209,51 @@ def get_slot_by_id(
     return event
 
 
-@app.post('/calendar_events/{slot_id}/mark_busy', response_model=CalendarEvent, tags=['Calendar'])
+class MarkBusyByIdResponse(SQLModel):
+    target_slot: CalendarEvent
+    target_slot_is_busy: bool
+    closest_free_slot: CalendarEvent | None
+    closest_free_slot_same_time: bool
+    closest_free_slot_same_day: bool
+
+
+@app.post('/calendar_events/{slot_id}/mark_busy', response_model=MarkBusyByIdResponse, tags=['Calendar'])
 def mark_busy_calendar_slot_by_id(
         slot_id: str,
         description: str | None = None,
         service: Resource = Depends(get_calendar_service)
 ):
     event = get_slot_by_id(slot_id=slot_id, service=service)
+    target_event_start_time = datetime.fromisoformat(event.start.dateTime)
 
-    if event.summary != TITLE_FREE:
-        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Slot is busy")
+    free_slots = get_free_calendar_slots(lower_bound=target_event_start_time, service=service)
+    free_slots = list(filter(lambda slot: slot.id != event.id, free_slots))
+    closest_free_slot = free_slots[0] if free_slots else None
+    closest_free_slot_same_time = False
+    closest_free_slot_same_day = False
+    if closest_free_slot:
+        closest_free_slot_start_time = datetime.fromisoformat(closest_free_slot.start.dateTime)
+        closest_free_slot_same_time = closest_free_slot_start_time == target_event_start_time
+        closest_free_slot_same_day = closest_free_slot_start_time.date() == target_event_start_time.date()
 
-    event.summary = TITLE_BUSY
-    event.colorId = COLOR_BUSY
-    if description:
-        event.description = description
+    target_slot_is_busy = False
+    if event.summary == TITLE_FREE:
+        event.summary = TITLE_BUSY
+        event.colorId = COLOR_BUSY
+        if description:
+            event.description = description
 
-    service.events().update(calendarId=CALENDAR_ID, eventId=event.id, body=event.dict(exclude_unset=True)).execute()
+        service.events().update(calendarId=CALENDAR_ID, eventId=event.id, body=event.dict(exclude_unset=True)).execute()
+    else:
+        target_slot_is_busy = True
 
-    return event
+    return MarkBusyByIdResponse(
+        target_slot=event,
+        target_slot_is_busy=target_slot_is_busy,
+        closest_free_slot=closest_free_slot,
+        closest_free_slot_same_time=closest_free_slot_same_time,
+        closest_free_slot_same_day=closest_free_slot_same_day
+    )
 
 
 @app.post('/calendar_events/{slot_id}/mark_free', response_model=CalendarEvent, tags=['Calendar'])
@@ -313,16 +339,15 @@ class FormatDateRequest(BaseModel):
                 {
                     'date': "10.07.2023 15:33:08"
                 }
-                # '2023-07-10T15:33:08+07:00',
-                # '2023-07-10 15:33:08',
-                # '10.07.2023 15:33:08'
             ]
         }
 
     @validator('date', pre=True)
     def validate_date(cls, val):
         try:
-            if re.match(r'^(\d{4}-\d{2}-\d{2}) (\d{2}:\d{2}:\d{2})$', val):
+            if type(val) == datetime:
+                return val
+            elif re.match(r'^(\d{4}-\d{2}-\d{2}) (\d{2}:\d{2}:\d{2})$', val):
                 return datetime.strptime(val, "%Y-%m-%d %H:%M:%S")
             elif re.match(r'^(\d{2}.\d{2}.\d{4}) (\d{2}:\d{2}:\d{2})$', val):
                 return datetime.strptime(val, "%d.%m.%Y %H:%M:%S")