public static int migratoryBirds(List<int> arr)
    {
        int mostFreq = 0;
        int id = 0;
        
        arr.GroupBy(id => id)
            .ToList()
            .ForEach(g => {
               Console.WriteLine(g.ToList().Count());
               int birsFre = g.ToList().Count();
               int currentId = g.First();
               if(birsFre > mostFreq) {
                    mostFreq = birsFre;
                    id = currentId; 
               }
               if(birsFre == mostFreq){
                    id = id < currentId ? id : currentId;
               }
            });
            
        return id;
    }