N = int(input())
S = input()
cnt = 0
first = 0
for i in range(N-1):
    if S[i+1]=="A":
        cnt+=1
    elif S[i]=="A":
        if i>=1 and S[i-1]=="B":
            pass
        else:
            cnt+=1
    elif first==0 and S[i]=="B" and S[i+1]=="B":
        first=1
        cnt+=1
print(cnt)