N = int(input())
S = input().strip()
S = "A"+S+"A"
cnt = 0
n0 = 0
n1 = 0
for i in range(1,N+1):
    if S[i]=="A":
        if S[i-1]==S[i+1]=="B":
            n0 += 1
        if cnt>0:
            n1 += cnt-1
            cnt = 0
    else:
        cnt += 1
if cnt>0:
    n1 += cnt-1
if n1==0:
    print(N-1-n0)
else:
    print(N-n0-n1)