N = int(input())
S = input()

ans = 0
for i in range(1, N):
    a, b = S[i-1], S[i]
    if a == b == 'B': continue
    if a == 'A' and b == 'B':
        if i-2 >= 0 and S[i-2] == 'B': continue
    ans += 1

if 'BB' in S:
    ans += 1

print(ans)