N = int(input())
S = list(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[c], S[d], S[e]])) == 4:
						ans += 1
print(ans)