n=int(input())
s=input()
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):
                    A=set([])
                    A.add(s[i])
                    A.add(s[j])
                    A.add(s[k])
                    A.add(s[l])
                    A.add(s[m])
                    if(len(A)==4 and s[i]== s[k]):
                        ans+=1
print(ans)