def main():
    n = int(input())
    S = input()
    ans = 0
    s = 0
    for i in range(n-1):
        if S[i]+S[i+1] == "BB":
            s = 1
        else:
            ans += 1
    for i in range(n-2):
        if S[i]+S[i+1]+S[i+2] == "BAB":
            ans -= 1
    return ans+s
print(main())