N = int(input())
S = list(input())
mod = 10**9+9
v = 0
for i,s in enumerate(S):
    if s=='B':
        v+=pow(2,i,mod)
ANS = set()
for i in range(N-1):
    temp = v
    if S[i]=='A':
        temp+=pow(2,i,mod)
    if S[i+1]=='A':
        temp+=pow(2,i+1,mod)
    ANS.add(temp)
print(len(ANS))