N = int(input())
S = input()

if N <= 4:
    exit(print(0))

def BIT(bit, n):
    return bit//27**n%27

def code(s):
    return ord(s)-ord("a")
def codeR(n):
    return chr(ord("a")+n)

ans = 0
for i in range(N-4):
    for j in range(i+2, N-2):
        if S[i] != S[j]:
            continue
        for k in range(i+1, j):
            for l in range(j+1, N-1):
                for m in range(l+1, N):
                    if len(set([S[i], S[k], S[l], S[m]])) == 4:
                        ans += 1

print(ans)