import sys


def input():
    return sys.stdin.readline().strip()


def main():
    n = int(input())
    s = input()

    ans = 0
    for a in range(n):
        for b in range(a + 1, n):
            for c in range(b + 1, n):
                for d in range(c + 1, n):
                    for e in range(d + 1, n):
                        if s[a] == s[c] and len(set((s[a], s[b], s[d], s[e]))) == 4:
                            ans += 1
    print(ans)


if __name__ == "__main__":
    main()