Problem:
Score : 600 points

Problem Statement

You are given a string s consisting of A, B and C.

Snuke wants to perform the following operation on s as many times as possible:

Choose a contiguous substring of s that reads ABC and replace it with BCA.

Find the maximum possible number of operations.

Constraints

1 \leq |s| \leq 200000

Each character of s is A, B and C.

Input

Input is given from Standard Input in the following format:

s

Output

Find the maximum possible number of operations.

Sample Input 1

ABCABC

Sample Output 1

3

You can perform the operations three times as follows: ABCABC → BCAABC → BCABCA → BCBCAA. This is the maximum result.

Sample Input 2

C

Sample Output 2

0

Sample Input 3

ABCACCBABCBCAABCB

Sample Output 3

6

Solution in C# (Mono 4.6.2.0) (judge verdict: Time Limit Exceeded)

using System;
using System.IO;
using System.Linq;

namespace AGC034
{
    class B
    {
        static void Main(string[] args)
        {

            //StreamReader sr = new StreamReader(@"testcase");
            //string s = sr.ReadLine();
            string s = Console.ReadLine();
            s = s.Replace("BC", "D");
            string[] S = s.Select(x => x.ToString()).ToArray();

            //Console.WriteLine(string.Join("", S));

            int count = 0;
            int index = 0;
            int res = 0;

            //string tmp;
            /* 
            for (int i = 0; i < S.Length - 1; i++)
            {
                if (S[i] == "A" && S[i + 1] == "D")
                {
                    tmp = S[i + 1];
                    S[i + 1] = S[i];
                    S[i] = tmp;
                    count++;
                }
            }
            */

            for (int i = S.Length - 2; i >= 0; i--)
            {
                if (S[i] == "A")
                {
                    index = i + 1;
                    while (index < S.Length && S[index] == "D")
                    {
                        index++;
                        count++;
                    }

                    if (0 < count)
                    {
                        S[i] = "D";
                        S[index - 1] = "A";
                    }
                    res += count;
                }
                count = 0;
            }
            Console.WriteLine(res);
        }
    }
}