n=int(input())
s=input()

if n<5:
	print(0)
	quit()

ans=0
for i in range(n-4):
	for j in range(i+2,n-2):
		if s[i]==s[j]:
			for x in s[i+1:j]:
				if x!=s[i]:
					t=s[j+1:].replace(s[i],"")
					t=t.replace(x,"")
					for k in range(len(t)):
						ans+=len(t[k+1:].replace(t[k],""))

print(ans)