N=int(input())
S=input()
ans=0
f=0
for i in range(N-1):
	if S[i]=="B" and S[i+1]=="B":
		f=1
	else:
		ans+=1
for i in range(N-2):
	if S[i:i+3]=="BAB":
		ans-=1
print(ans+f)