import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        char[] inputs = sc.next().toCharArray();
        int a = 0;
        long total = 0;
        for (int i = 0; i < n; i++) {
            if (inputs[i] == 'C') {
                total += a;
            } else {
                a++;
            }
        }
        long ans = total;
        int c = 0;
        for (int i = n - 1; i >= 0; i--) {
            if (inputs[i] == 'C') {
                c++;
            } else if (inputs[i] == 'A') {
                a--;
            } else {
                total -= c;
                a--;
                c++;
                total += a;
                ans = Math.max(ans, total);
            }
        }
        System.out.println(ans);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}