import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        sc.nextLine();
        String s = sc.nextLine();
        char[] p = {'A', 'B', 'C'};
        int idx = 0;
        int count = 0;

        for (int i = 0; i < n; i++) {
            if (s.charAt(i) != p[idx]) {
                idx = s.charAt(i) == p[0] ? 1 : 0;
            }
            else idx++;
            if (idx == 3) {
                idx = 0;
                count++;
            }
        }
        System.out.println(count);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz