N = int(input())
S = list(input())
# N = len(S)
if N == 2:
	print(1)
	exit()

T = []
c = 1
for i in range(1,N):
	if S[i] == S[i-1]:
		c += 1
	else:
		T.append([S[i-1],c])
		c = 1
T.append([S[-1],c])
# print(T)

M = len(T)
ans = N - 1
X = 0
for j in range(M):
	if T[j][0] == 'B':
		if T[j][1] >= 2:
			X += T[j][1] - 1
if X > 0:
	ans -= X - 1

for j in range(1,M-1):
	if T[j][0] == 'A':
		if T[j][1] == 1:
			if (T[j-1][0] == 'B') & (T[j+1][0] == 'B'):
				ans -= 1

print(ans)