import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.NoSuchElementException;

public class Main implements Runnable { 
	    public static void main(String[] args) {
	        new Thread(null, new Main(), "", Runtime.getRuntime().maxMemory()).start(); 
	    }
	    
	    final long mod = 998244353;
	    
	    public void run() {
	    	FastScanner sc=new FastScanner();
	    	PrintWriter pw=new PrintWriter(System.out);
	    	int N=sc.nextInt();
	    	char[] cs=sc.next().toCharArray();
	    	int ans=N-1;
	    	int unchanged = 0;
	    	for (int i=0;i + 1<cs.length;++i) {
	    		if (cs[i] == 'B' && cs[i + 1] == 'B') ++unchanged;
	    		if (cs[i] == 'A' && cs[i + 1] == 'A') continue;
	    	}
	    	for (int i=0;i+2<cs.length;++i) {
	    		char a=cs[i];
	    		char b=cs[i+1];
	    		char c=cs[i+2];
	    		if (a=='B'&&b=='A'&&c=='B') --ans;
	    	}
	    	ans -= Math.max(0, unchanged - 1);
	    	pw.println(ans);
	    	pw.close();
	    }
	    
		void tr(Object...objects) {System.err.println(Arrays.deepToString(objects));}	
	}
	
	class FastScanner {
	    private final InputStream in = System.in;
	    private final byte[] buffer = new byte[1024];
	    private int ptr = 0;
	    private int buflen = 0;
	    private boolean hasNextByte() {
	        if (ptr < buflen) {
	            return true;
	        }else{
	            ptr = 0;
	            try {
	                buflen = in.read(buffer);
	            } catch (IOException e) {
	                e.printStackTrace();
	            }
	            if (buflen <= 0) {
	                return false;
	            }
	        }
	        return true;
	    }
	    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
	    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
	    public String next() {
	        if (!hasNext()) throw new NoSuchElementException();
	        StringBuilder sb = new StringBuilder();
	        int b = readByte();
	        while(isPrintableChar(b)) {
	            sb.appendCodePoint(b);
	            b = readByte();
	        }
	        return sb.toString();
	    }
	    public long nextLong() {
	        if (!hasNext()) throw new NoSuchElementException();
	        long n = 0;
	        boolean minus = false;
	        int b = readByte();
	        if (b == '-') {
	            minus = true;
	            b = readByte();
	        }
	        if (b < '0' || '9' < b) {
	            throw new NumberFormatException();
	        }
	        while(true){
	            if ('0' <= b && b <= '9') {
	                n *= 10;
	                n += b - '0';
	            }else if(b == -1 || !isPrintableChar(b)){
	                return minus ? -n : n;
	            }else{
	                throw new NumberFormatException();
	            }
	            b = readByte();
	        }
	    }
	    public int nextInt() {
	    	return (int)nextLong();
	    }
	}