n = int(input())
s = input()
result = 0

n = len(s)
for i in range(n):
    for j in range(i + 1, n):
        if s[i] == s[j]:
            continue
        for k in range(j + 1, n):
            if s[i] != s[k] or s[j] == s[k]:
                continue
            for l in range(k + 1, n):
                if s[l] in (s[i], s[j], s[k]):
                    continue
                for m in range(l + 1, n):
                    if s[m] in (s[i], s[j], s[k], s[l]):
                        continue
                    result += 1

print(result)