N=int(input())
S=input().strip()

ANS=0

for i in range(len(S)):
    for j in range(i+1,len(S)):
        for k in range(j+1,len(S)):
            for l in range(k+1,len(S)):
                for m in range(l+1,len(S)):
                    A=[S[i],S[j],S[k],S[l],S[m]]

                    if A[0]==A[2] and len(set(A))==4:
                        ANS+=1

print(ANS)