n = int(input())
s = input()

count = 0
for i1 in range(n):
    for i2 in range(i1 + 1, n):
        for i3 in range(i2 + 1, n):
            for i4 in range(i3 + 1, n):
                for i5 in range(i4 + 1, n):
                    if s[i1] == s[i3] and len({s[i1], s[i2], s[i4], s[i5]}) == 4:
                        count += 1

print(count)