from collections import Counter
n = int(input())
s = input()
ans = 0
for i in range(n):
	si = i
	while True:
		nxt_si = -1
		for j in range(si+1, n):
			if s[j]==s[i]:
				nxt_si = j
				break
		if nxt_si == -1:
			break
		si = nxt_si
		prev_cnt = Counter(list(s[i+1:si]))
		prev_cnt.subtract({s[i]: prev_cnt[s[i]]})
		aftr_cnt = Counter(list(s[si+1:]))
		aftr_cnt.subtract({s[i]: aftr_cnt[s[i]]})
		
		for k, v in prev_cnt.items():
			av = aftr_cnt[k]
			aftr_cnt.update({k: -av})
			t = sum(aftr_cnt.values())
			res = 0
			for val in aftr_cnt.values():
				res += val*(t-val)
			ans += prev_cnt[k]*(res // 2)
			# print(k,t, res//2)
			aftr_cnt.update({k:av})
		# print(i, si, ans)
		# print(prev_cnt, aftr_cnt)
print(ans)