import sys
sys.setrecursionlimit(500000)
#import pypyjit
#pypyjit.set_param('max_unroll_recursion=-1')
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def TI(): return tuple(map(int,sys.stdin.readline().rstrip().split()))
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def SI(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip())
#for i, pi in enumerate(p):
from collections import defaultdict,deque
import bisect
import itertools
dic = defaultdict(int)
d = deque()
YN = ['No','Yes']

N = I()
S = LS()
ans = 0
count = 0
for j,i in enumerate(S):
  if i == 'A':
    count += 1
  elif i == 'C':
    ans += count
  else:
    count += 1
x = 0
for i in range(N-1,-1,-1):
  si = S[i]
  if si == 'A':
    count -= 1
   
  elif si == 'C':
    x += 1
    continue
  else:
    count -= 1
    if ans < ans - x + count:
      ans = ans-x+count
      x += 1
print(ans)