n=int(input())
s=input()
c=0
for p1 in range(n):
	for p2 in range(n):
		for p3 in range(n):
			for p4 in range(n):
				for p5 in range(n):
					if p1<p2<p3<p4<p5:
						c+=s[p1]==s[p3] and len([s[p1],s[p2],s[p3],s[p4],s[p5]])==4
print(c)