# import sys
# sys.setrecursionlimit(10**7)
# input = sys.stdin.readline
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
def mp():return map(int,input().split())
def lmp():return list(map(int,input().split()))
def mps(A):return [tuple(map(str, input().split())) for _ in range(A)]
def stoi(LIST):return list(map(int,LIST))
def itos(LIST):return list(map(str,LIST))
def atoi(LIST): return [ord(i)-ord("a") for i in LIST]
def Atoi(LIST): return [ord(i)-ord("A") for i in LIST]
def bitA(X,A):return X & 1<<A == 1<<A
import math
import bisect
import heapq
import time
from copy import copy as cc
from copy import deepcopy as dc
from itertools import accumulate, product
from collections import Counter, defaultdict, deque
def ceil(U,V):return (U+V-1)//V
def modf1(N,MOD):return (N-1)%MOD+1
inf = int(1e18)+20
mod = int(1e9+7)
def rle(lst):
    ans = []
    cnt = 1
    ini = lst[0]
    for i in range(1, len(lst)):
        if ini == lst[i]:cnt += 1
        else:
            ans.append((ini, cnt))
            cnt = 1
            ini = lst[i]
    ans.append((ini, cnt))
    return ans

n = int(input())
s = list(input())

ans = 0
sr = rle(s)
sj = "".join(s)
if len(sr) == 1 and sr[0][0] == "A":
    print(sr[0][1]-1)
    exit()
for c,(i,j) in enumerate(sr):
    if c == 0 and i == "A":
        if j == 1:ans += 1
        else:ans += j
    elif c == len(sr)-1 and i == "A":
        if j == 1:ans += 1
        else:ans += j
    elif i == "A":
        if j == 1:ans += 1
        else:ans += j+1
if "BB" in sj:ans += 1
print(ans)