N = int(input())
S = input()
ans = 0

prea = 0
sufc = 0
for x in S :
    if x != 'A' :
        sufc += 1

for x in S :
    if x != 'A' :
        sufc -= 1
    if x != 'C' :
        prea += 1
    ans += min(prea, sufc)

print(ans)