import sys
input = sys.stdin.readline

def solve():
    N = int(input())
    S = input().strip()
    ans = 0

    # range(N) から5つ選ぶ全組み合わせ（i<j<k<l<m）を列挙
    for i in range(N):
        for j in range(i+1, N):
            for k in range(j+1, N):
                # 1文字目と3文字目が等しいこと
                if S[i] != S[k]:
                    continue
                for l in range(k+1, N):
                    # S[l]（4文字目）が S[i], S[j] と重複しないこと
                    if S[l] == S[i] or S[l] == S[j]:
                        continue
                    for m in range(l+1, N):
                        # S[m]（5文字目）が S[i], S[j], S[l] と重複しないこと
                        if S[m] == S[i] or S[m] == S[j] or S[m] == S[l]:
                            continue
                        # ここまでくれば必ず
                        # S[i]==S[k], かつ b=S[j], d=S[l], e=S[m] は互いに全て異なる
                        ans += 1

    print(ans)

if __name__ == "__main__":
    solve()