package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Buffer(make([]byte, 6+2+200000+2), 6+2+200000+2)
	sc.Scan()
	N, _ := strconv.Atoi(sc.Text())
	sc.Scan()
	S := sc.Text()

	count := 0
	count1 := 0
	for i := 0; i+2 <= N; i++ {
		if S[i:i+2] == "BB" {
			count1 = 1
		} else if S[i:i+2] != "AB" || i == 0 || S[i-1] == 'A' {
			count++
		}
	}
	fmt.Println(count1 + count)
}