import java.io.*;
import java.util.*;
public class Main{
    static int N = 1000010;
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int k = Integer.parseInt(br.readLine());
        String s = br.readLine();
        s += ".";
        List<Integer> Alice = new ArrayList();
        List<Integer> Bob = new ArrayList();

        StringBuilder tem = new StringBuilder();
        for(int i=0; i<s.length(); i++){

            if(! (Character.isLetter( s.charAt(i)) ) ){
                String str = tem.toString();
                if(str.equals("Alice")) Alice.add( i-tem.length() );
                if(str.equals("Bob"))   Bob.add( i-tem.length() );
                tem.delete(0,tem.length());
            }else{
                tem.append(s.charAt(i));
            }
        }
        long res = 0;
        int n = Alice.size();
        int m = Bob.size();
        int l = 0,r = m-1 ;
        for(int i=0; i<n; i++){
            while(l<m && Bob.get(l) < Alice.get(i) - k -3 ) l++;
            r = l;
            while(r<m && Bob.get(r) <= Alice.get(i) + 5 +k ) r++;
            if(r-l > 0) res += r-l;
        }
        System.out.println(res);
    }
}