n = int(input())
S = input()

ans = 0
i = 0
flag = False
while i < n - 1:
    if i < n - 2 and S[i] == 'B' and S[i + 1] == 'A' and S[i + 2] == 'B':
        ans += 1
        i += 2
    elif S[i] == 'B' and S[i + 1] == 'B':
        if not flag:
            ans += 1
            flag = True
        i += 1
    else:
        ans += 1
        i += 1
print(ans)