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 t in range(k+1,N):
                for l in range(t+1,N):
                    s = S[i]+S[j]+S[k]+S[t]+S[l]
                    if len({si for si in s})==4 and S[i] == S[k]:
                        ans+=1
print(ans)