n=int(input())
s=list(input())
ans=0
f = 0

for i in range(n):
    if i - 2 >= 0:
        if s[i] ==  'B' and s[i-2] == 'B' and s[i-1] == 'A':
            ans -= 1
            
    if i < n-1:
        if s[i] == 'B' and s[i+1] == 'B':
            if f==0:
                ans+=1
            f=1
            
        else:
            ans+=1

print(ans)