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 Lua (Lua 5.3.5) (judge verdict: Accepted)

local str = io.read()
local ans = 0
local tbl = {}
for cur=1, string.len(str) do
	tbl[cur] = string.sub(str,cur,cur)
end
local used = {}
local cur = 1
local Anum = 0
while cur <= #tbl -2 do
	local flag = false
	if tbl[cur] == "A" and tbl[cur+1] == "B" and tbl[cur+2] == "C" then

		ans = ans + 1
		tbl[cur] = "B"
		tbl[cur+1] = "C"
		tbl[cur+2] = "A"
		-- l = cur -1 
		-- while l > 0 and tbl[l] == "A"  do
		-- 	flag = true
		-- 	ans = ans + 1
		-- 	tbl[l] = "B"
		-- 	tbl[l+1] = "C"
		-- 	tbl[l+2] = "A"
		-- 	l = l - 1
		-- end
		-- print("######", Anum)
		if Anum > 0 then
			ans = ans + Anum
			tbl[cur +1] = "A"
			if Anum > 1 then
				tbl[cur] = "A"
			end
			Anum = Anum - 1
		end
	elseif tbl[cur] == "A" then
		if cur - 1 > 0 and tbl[cur - 1] == "A" then
			Anum = Anum + 1
		else
			Anum = 1
		end
	else
		Anum = 0
	end

    cur = cur + 1
end
print(ans)