import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const S = readToken;
      
      auto sumA = new int[N + 1];
      auto sumC = new int[N + 1];
      foreach (i; 0 .. N) {
        sumA[i + 1] = sumA[i] + ((S[i] == 'A') ? 1 : 0);
        sumC[i + 1] = sumC[i] + ((S[i] == 'C') ? 1 : 0);
      }
      long base;
      foreach (i; 0 .. N) if (S[i] == 'C') {
        base += sumA[i];
      }
      
      long[] fs, gs;
      foreach (i; 0 .. N) if (S[i] == '?') {
        fs ~= (sumC[N] - sumC[i]);
        gs ~= sumA[i];
      }
      const len = cast(int)(fs.length);
      auto head = new long[len + 1];
      auto tail = new long[len + 1];
      foreach (j; 0 .. len) head[j + 1] = head[j] + fs[j];
      foreach_reverse (j; 0 .. len) tail[j] = gs[j] + tail[j + 1];
      debug {
        writeln("fs = ", fs);
        writeln("gs = ", gs);
        writeln("head = ", head);
        writeln("tail = ", tail);
      }
      
      long ans;
      foreach (j; 0 .. len + 1) {
        const score = base + head[j] + tail[j] + 1L * j * (len - j);
        debug {
          writeln(j, ": ", score);
        }
        chmax(ans, score);
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}