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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
static class Program{
	const int mod=(int)1e9+7;
	static void Main(){
		Sc sc=new Sc();
		//int[] s=sc.Ia;
		string t=sc.S;
		int ans=0,p=0;
		char c='B';
		for(int i = t.Length-1;i>=0;i--) {
			if(t[i]=='A'){
				if(c=='C'){
					p=0;
					c=t[i];
				}
				else{ans+=p;}
				continue;
			}
			if(t[i]=='B'&&c=='C'){
				p++;
			}
			else if(t[i]=='C'&&c=='B'){
				
			}
			else{p=0;}
			c=t[i];
			//Console.WriteLine("{0} {1}",t[i],p);

		}
		Console.WriteLine("{0}",ans);
	}
}

public class Sc{
	private string[] a;
	private int n=-1,m=0;
	public int I{get{if(n==-1||n==a.Length-1){n=-1;a=Console.ReadLine().Split();}n++;return int.Parse(a[n]);}}
	public long L{get{if(n==-1||n==a.Length-1){n=-1;a=Console.ReadLine().Split();}n++;return long.Parse(a[n]);}}
	public double D{get{if(n==-1||n==a.Length-1){n=-1;a=Console.ReadLine().Split();}n++;return double.Parse(a[n]);}}
	public string S{get{if(n==-1||n==a.Length-1){n=-1;a=Console.ReadLine().Split();}n++;return a[n];}}
	public string Sz{get{return Console.ReadLine();}}
	public int[] Ia{get{if(n!=-1&&n!=a.Length-1){m=n;n=-1;return Array.ConvertAll(a.Skip(m+1).ToArray(),int.Parse);}return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public int[] Ia2(int b){return Array.ConvertAll((((b&1)!=0?"0 ":"")+Console.ReadLine()+((b&2)!=0?" 0":"")).Split(),int.Parse);}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public string[] Sa2{get{return (Console.ReadLine()+" 0").Split();}}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
}