mod = 998244353


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    S = input().rstrip('\n')

    cnt = 0
    cnt2 = 0
    for i in range(N - 1):
        if S[i] == S[i+1] == "B":
            cnt += 1
        else:
            if i + 2 < N:
                if S[i] == "B" and S[i+1] == "A" and S[i+2] == "B":
                    cnt2 += 1
    print(N - 1 - max(0, cnt - 1) - cnt2)


if __name__ == '__main__':
    main()