N = int(input())
ans = 0
S = input()
for i in range(N):
	for j in range(i+1,N):
		for k in range(j+1,N):
			for l in range(k+1,N):
				for m in range(l+1,N):
					if(S[i] == S[k]):
						st = set()
						st.add(S[i])
						st.add(S[j])
						st.add(S[k])
						st.add(S[l])
						st.add(S[m])
						if(len(st) == 4):
							ans += 1
print(ans)