import macros
macro Please(x): untyped = nnkStmtList.newTree()

Please use Nim-ACL
Please use Nim-ACL
Please use Nim-ACL



#[ include daylight/base ]#
when not declared DAYLIGHT_BASE_HPP:
    const DAYLIGHT_BASE_HPP* = 1
    import system
    import macros
    import algorithm
    import tables
    import sets
    import lists
    import intsets
    import critbits
    import sequtils
    import strutils
    import std/math
    import strformat
    import sugar
    let readToken* = iterator(oneChar: bool = false): string {.closure.}= 
        while true:
            var line = stdin.readLine.split
            for s in line:
                if oneChar:
                    for i in 0..<s.len():
                        yield s[i..i]
                else:
                    yield s
    proc read*(t: typedesc[string]): string = 
        result = readToken()
        while result == "":
            result = readToken()
    proc read*(t: typedesc[int]): int = read(string).parseInt
    proc read*(t: typedesc[float]): float = read(string).parseFloat
    proc read*(t: typedesc[char]): char = readToken(true)[0]

    macro readSeq*(t: typedesc, n: varargs[int]): untyped =
        var repStr = ""
        for arg in n:
            repStr &= &"({arg.repr}).newSeqWith "
        parseExpr(&"{repStr}read({t})")
    
    macro read*(ts: varargs[auto]): untyped=
        var tupStr = ""
        for t in ts:
            tupStr &= &"read({t.repr}),"
        parseExpr(&"({tupStr})")
        
    macro readTupleSeq*(n: int, ts:varargs[auto]): untyped=
        for typ in ts:
            if typ.typeKind != ntyAnything:
                error("Expected typedesc, got " & typ.repr, typ)
        parseExpr(&"({n.repr}).newSeqWith read({ts.repr})")
        
    macro initSeq*(t: typedesc, n: varargs[int]): untyped =
        var repStr = ""
        for i, arg in n:
            if i == n.len - 1:
                repStr &= &"newSeq[{t}]({arg.repr}) "
            else:
                repStr &= &"({arg.repr}).newSeqWith "
        parseExpr(repStr)
    
    
    proc `-`*(a,b: char): int = ord(a) - ord(b)
    proc `+`*(a: char,b: int): char = char(ord(a) + b)
    proc `-`*(a: char,b: int): char = char(ord(a) - b)
    proc `++`*(a: var int) = a += 1
    proc `--`*(a: var int) = a += 1

    proc chmin*[T](a: var T, b: T): bool {.discardable.} =
        if a > b:
            a = b
            return true
        return false
    
    proc chmax*[T](a: var T, b: T): bool {.discardable.} =
        if a < b:
            a = b
            return true
        return false
    const INF* = (1e9+100).int
    const LINF* = (4e18 + 100).int
    discard

proc solve() =
    var
        N = read(int)
        S = read(string)
        cntA = 0
        cntC = 0
        ans = 0
    for i in 0..<N:
        if S[i] == 'A':
            cntA += 1
        else:
            cntC += 1
            ans += cntA
    var cur = ans
    cntA = 0
    for i in 0..<N:
        if S[i] == 'A':
            cntA += 1
        elif S[i] == 'C':
            cntC -= 1
        else:
            cntC -= 1
            cur += cntC
            cur -= cntA
            cntA += 1
        ans.chmax(cur)
    echo ans


solve()