def RunLengthEncoding(S):
    res = []
    N = len(S)
    i = 0
    while i < N:
        cnt = 1
        while i < N - 1 and S[i] == S[i + 1]:
            cnt += 1
            i += 1
        res.append((S[i], cnt))
        i += 1
    return res


N = int(input())
S = input()


ans = 0
bb = 0

RLE = RunLengthEncoding(S)

for i, (k, v) in enumerate(RLE):
    if k == "A":
        ans += v - 1
        if v == 1:
            ans += 1
        else:
            ans += i > 0
            ans += i < len(RLE) - 1
    else:
        if v > 1:
            bb = 1

print(ans + bb)