using System;

internal static class Program
{
    private static void Main(string[] args)
    {
        Console.WriteLine($"Total: {AddCount(5, 4)}");
        Console.WriteLine($"Overflow rejected: {AddCount(int.MaxValue, 1) is null}");
    }

    internal static int? AddCount(int current, int extra)
    {
        if (current < 0 || extra < 0) return null;
        try { return checked(current + extra); }
        catch (OverflowException) { return null; }
    }
}