n = int(input())
S = input()
numA = 0
base = 0
for s in S:
    if s == "A":
        numA += 1
    else:
        base += numA

ans = base
numC = n-numA
numA = 0
for s in S:
    if s == "A":
        numA += 1
    elif s == "C":
        numC -= 1
    else:

        base -= numA
        numA += 1
        numC -= 1
        base += numC

        ans = max(ans,base)
print(ans)