n=int(input())
if n<5:
	print(0)
	quit()
s=input()
ans=0
for i in range(n-4):
	for j in range(i+1,n-2):
		if s[i]==s[j]:
			if set(s[i+1:j]) > set(s[j+1:]) or len(set(s[j+1:]))>3:
				ans+=1
print(ans)