n = int(input())
s = input()
res = 0
for i in range(n):
	for j in range(i+1, n):
		if s[i] == s[j]: continue
		for k in range(j+1, n):
			if s[i] != s[k]: continue
			if s[j] == s[k]: continue
			for l in range(k+1, n):
				if s[i] == s[l]: continue
				if s[j] == s[l]: continue
				for m in range(l+1, n):
					if s[i] == s[m]: continue
					if s[j] == s[m]: continue
					if s[l] == s[m]: continue
					res += 1

print(res)