n = int(input())
s = input()
s1 = [ 0 ] * (n + 1)
s2 = [ 0 ] * (n + 1)
s3 = [ 0 ] * (n + 1)
for i in range(n):
	s1[i + 1] = s1[i] + (s[i] == 'A')
	s2[i + 1] = s2[i] + (s[i] == 'C')
	s3[i + 1] = s3[i] + (s[i] == '?')
t = list(s)
for i in range(n):
	if s[i] == '?':
		na = s1[i] + s3[i]
		nc = (s2[n] - s2[i + 1]) + (s3[n] - s3[i + 1])
		t[i] = ('A' if na <= nc else 'C')
numa = 0
answer = 0
for i in range(n):
	numa += (t[i] == 'A')
	if t[i] == 'C':
		answer += numa
print(answer)