public static int migratoryBirds(List<int> arr)
    {
        var birdsDict = new Dictionary<int, int>();
        for(var i = 0; i < arr.Count; i++){
            if(birdsDict.ContainsKey(arr[i])){
                birdsDict[arr[i]] ++;
                continue;
            }
            birdsDict.Add(arr[i],  1);
        }
        
        var maxSightings = birdsDict.Values.Max();
        var minId = birdsDict.Where(x => x.Value == maxSightings).Min(z => z.Key);
        return minId;
    }