def count_cpctf_subsequences(S):
    N = len(S)
    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):
                        c1, c2, c3, c4, c5 = S[i1], S[i2], S[i3], S[i4], S[i5]
                        if c1 != c3:
                            continue
                        # c2, c4, c5 が c1 と重複しない、かつ相互に異なる
                        if len({c2, c4, c5}) == 3 and c1 not in {c2, c4, c5}:
                            count += 1
    return count

n = int(input())
S = input()

print(count_cpctf_subsequences(S))