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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        ArrayList<Character> list = new ArrayList<>();
        int[] counts = new int[26];
        for (char c : sc.next().toCharArray()) {
            list.add(c);
            counts[c - 'A']++;
        }
        String agct = "AGCT";
        int[] idxes = new int[4];
        for (int i = 0; i < 4; i++) {
            idxes[i] = agct.charAt(i) - 'A';
        }
        int ans = 0;
        int plus = 0;
        while (true) {
            int current = 0;
            for (int x : idxes) {
                current += counts[(x + plus) % 26];
            }
            if (current == 0) {
                break;
            }
            char c = list.get(current - 1);
            counts[c - 'A']--;
            list.remove(current - 1);
            plus += 26 - counts[c - 'A'] % 26;
            plus %= 26;
            ans++;
        }
        System.out.println(ans);
    }
}

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();
    }
    
}