N=int(input())
S=input()
ans=0
cnt=-1
for i in range(N-1):
    if i+2<N and S[i]=="B" and S[i+1]=="A" and S[i+2]=="B":
        ans+=1
    if S[i]==S[i+1]=="B":
        cnt+=1
print(N-1-max(0,cnt)-ans)