N = int(input())
S = input()
f = False
cnt = 0
for i in range(N-4):
    for j in range(i+1,N-3):
        for k in range(j+1,N-2):
            #print(i,j,k)
            if S[i]==S[j]:
                break
            if (S[i]!=S[k]):
                
                continue
            for l in range(k+1,N-1):
                for m in range(l+1,N):
                    
                    if (S[i]!=S[l]) and (S[i]!=S[m]) and (S[j]!=S[l]) and (S[j]!=S[m]) and (S[l]!=S[m]):
                        #print(i,j,k,m,l)
                        cnt += 1



print(cnt)