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

mask = 10000000
w = set()
for i in range(n-1):
	tmp = []
	if s[i] == "A":
		tmp.append(i+1)
	if s[i+1] == "A":
		tmp.append(i+2)
	v = 1
	l = 0
	for j in tmp:
		l += v * j
		v *= mask
	w.add(l)

print(len(w))