import sys, random
input = lambda : sys.stdin.readline().rstrip()


write = lambda x: sys.stdout.write(x+"\n"); writef = lambda x: print("{:.12f}".format(x))
debug = lambda x: sys.stderr.write(x+"\n")
YES="Yes"; NO="No"; pans = lambda v: print(YES if v else NO); INF=10**18
LI = lambda : list(map(int, input().split())); II=lambda : int(input()); SI=lambda : [ord(c)-ord("a") for c in input()]
def debug(_l_):
    for s in _l_.split():
        print(f"{s}={eval(s)}", end=" ")
    print()
def dlist(*l, fill=0):
    if len(l)==1:
        return [fill]*l[0]
    ll = l[1:]
    return [dlist(*ll, fill=fill) for _ in range(l[0])]

n = int(input())
s = input()
a = [0]*n
index = []
vs0 = []
vs1 = []
v0 = v1 = 0
res = 0
for i in range(n):
    if s[i]=="C":
        a[i] = 1
        v1 += 1
        res += v0
    elif s[i]=="A":
        a[i] = 0
        v0 += 1
    else:
        a[i] = -1
        index.append(i)
        vs0.append(v0)
        vs1.append(v1)
s = len(index)
vs1 = [v1-v for v in vs1]
cum = [0]*(s+1)
cum1 = [0]*(s+1)
for i in range(s)[::-1]:
    cum[i] = cum[i+1] + vs0[i]
for i in range(s):
    cum1[i+1] = cum1[i] + vs1[i]
ans = -INF
for i in range(s+1):
    val = cum[i] + i * (s-i) + cum1[i]
    ans = max(val,ans)
print(ans+res)