N = int(input())
S = input()
ans = 0
for i in range(N):
	for j in range(i+1,N):
		for k in range(j+1,N):
			for x in range(k+1,N):
				for y in range(x+1,N):
					if S[i] == S[k] and len({S[i],S[j],S[j],S[x],S[y]}) == 4:
						ans += 1
print(ans)