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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include "bits/stdc++.h"
using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)   FOR(i,0,n)
#define ALL(a)  (a).begin(),(a).end()
#define LL long long
string s;
int main(){
  cin>>s;
  int n = s.size();
  LL cnt=0;
  LL ret=0;
  int idx=0;
  while(idx < n-1){
    if(s[idx]=='A'){
      cnt++;
      idx++;
    }else if(s[idx]=='B' && s[idx+1]=='C'){
      ret+=(LL)cnt;
      idx+=2;
    }else{
      idx++;
    }
  }
  cout<<ret<<endl;
  return 0;
}