n = int(input())
s = input()

cnt, bb = 0, 0
for i in range(n-1):
    if s[i] + s[i+1] == "BB":
        bb = 1
    else:
        cnt += 1

for i in range(n-2):
    if s[i:i+3] == "BAB":
        cnt -= 1

print(cnt+bb)