N=int(input())
S=input()
if N<5:
	print(0)
	exit()
ans=0
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):
					P=[S[i],S[j],S[k],S[l],S[m]]
					ok=1
					for s in range(5):
						for t in range(s+1,5):
							if P[s]==P[t]:
								if s!=0 or t!=2:
									ok=0
							else:
								if s==0 and t==2:
									ok=0
					ans+=ok
print(ans)