import itertools

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

A = [(k, len(list(g))) for k, g in itertools.groupby(s)]

ans = 0
for i in range(len(A)):
    if A[i][0] == "A":
        if A[i][1] == 1:
            ans += 1
        else:
            ans += A[i][1] + 1

ans += "BB" in s
ans -= A[0][0] == "A" + A[-1][0] == "A"

print(ans)