n = int(input())
s = input().strip()

unique = set()

for i in range(n - 1):
    a, b = s[i], s[i+1]
    current = []
    if a == 'A':
        current.append(i)
    if b == 'A':
        current.append(i+1)
    unique.add(tuple(current))

print(len(unique))