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
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
	end
    cur = cur + 1
end
print(ans)
