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

public class Main {
    static long ans = 0;
    static char[] inputs;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        inputs = sc.next().toCharArray();
        aac(0, 0, 0);
        System.out.println(ans);
    }
    
    static void aac(int idx, long a, long value) {
        if (idx == inputs.length) {
            ans = Math.max(ans, value);
            return;
        }
        if (inputs[idx] == 'A') {
            aac(idx + 1, a + 1, value);
        } else if (inputs[idx] == 'C') {
            aac(idx + 1, a, value + a);
        } else {
            aac(idx + 1, a + 1, value);
            cac(idx + 1, a, value + a);
        }
    }
    
    static void cac(int idx, long a, long value) {
        if (idx == inputs.length) {
            ans = Math.max(ans, value);
            return;
        }
        if (inputs[idx] == 'A') {
            cac(idx + 1, a + 1, value);
        } else if (inputs[idx] == 'C') {
            cac(idx + 1, a, value + a);
        } else {
            cac(idx + 1, a, value + a);
        }
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}