How do I convert this double foreach loop to just lambdas?

Is this there a way to these foreach loops just one lambda expression?

    private int getNextEventId()
     {
         int numOfEvents = 0;
 
         foreach (MonthModel eventMonth in eventsForAllMonths)
         {
             foreach (DayModel eventDay in eventMonth.AllDays)
             {
                 numOfEvents += eventDay.CalEvents.Count;
             }
         }
 
         return numOfEvents + 1;
     }
 

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