import re
n=int(input())
s=input()
bb=-1
for i in range(n-1):
	if s[i]==s[i+1] and s[i]=="B":
		bb+=1
ans=n-1-max(bb,0)
bab=0
for i in range(n-2):
	if s[i:i+3]=="BAB":
		bab+=1
ans-=bab
print(ans)