local mmi, mma = math.min, math.max
local n = io.read("*n", "*l")
local s = io.read()
local acnt = 0
local base = 0
local ta, tc = {}, {}
for i = 1, n do
  local b = s:sub(i, i)
  if b == "A" then
    acnt = acnt + 1
  elseif b == "C" then
    base = base + acnt
  else
    table.insert(ta, acnt)
  end
end

local ccnt = 0
local tmp = #ta
for i = n, 1, -1 do
  local b = s:sub(i, i)
  if b == "A" then
    tmp = tmp - 1
  elseif b == "C" then
    ccnt = ccnt + 1
  else
    table.insert(tc, ccnt)
    base = base + ta[tmp]
  end
end
for i = 1, #ta do
  local j = #ta + 1 - i
  if j <= i then break end
  tc[i], tc[j] = tc[j], tc[i]
end

local cand = base
for i = 1, #ta do
  base = base - ta[i] + tc[i]
  cand = mma(cand, base + i * (#ta - i))
end
print(cand)