n = int(input())
s = list(input().rstrip())
ans = 0
import string
for a in string.ascii_uppercase:
    for b in string.ascii_uppercase:
        for c in string.ascii_uppercase:
            for d in string.ascii_uppercase:
                if a == b or a == c or a == d or b == c or b == d or c == d:continue
                temp = [0 for j in range(5)]
                for i in s:
                    if i == a:
                        temp[2] += temp[1]
                        temp[0] += 1
                    if i == b:
                        temp[1] += temp[0]
                    if i == c:
                        temp[3] += temp[2]
                    if i == d:
                        temp[4] += temp[3]
                ans += temp[-1]
print(ans)