NationWords.cs

using System;
using System.Linq;

namespace _4Phil
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Testing algorithm...");
            Console.WriteLine(NumberOfACharAdditions("baaa"));
            Console.WriteLine(NumberOfACharAdditions("aa"));
            Console.WriteLine(NumberOfACharAdditions("dog"));
            Console.WriteLine(NumberOfACharAdditions("aabab"));
        }

        static private int NumberOfACharAdditions(string aString)
        {
            // Fail fast
            if ("aa" == aString)
            {
                return 0;
            }
            
            if (aString.Contains("aaa"))
            {
                return -1;
            }

            // Return the number of a additions
            int numberOfNonAChars = aString.Count(c => (c != 'a'));
            int numberOfAChars = aString.Count(c => (c == 'a'));

            return ((numberOfNonAChars * 2) + 2) - numberOfAChars;
        }
    }
}