[STAThread]
static void Main()
{
Int32 M, N, max;
max = Int32.MinValue;
N = Int32.Parse(Console.ReadLine());
for (int i = 0; i < N; i++)
{
M = Int32.Parse(Console.ReadLine());
if ((max < M) && (M > 0))
max = M;
}
Console.WriteLine(max == int.MinValue ? ":(" : max.ToString());
Console.ReadLine();
}