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

max_right_c = [0] * (n + 1)

for i in range(n - 1, -1, -1):
    if s[i] == 'C' or s[i] == '?':
        max_right_c[i] = max_right_c[i + 1] + 1
    else:
        max_right_c[i] = max_right_c[i + 1]

a = 0
total = 0

for i in range(n):
    if s[i] == 'A':
        a += 1
    elif s[i] == 'C':
        total += a
    else:
        # It's '?', decide between A or C
        current_max_right = max_right_c[i + 1] if i + 1 < n else 0
        if a >= current_max_right:
            total += a
        else:
            a += 1

print(total)