from collections import defaultdict
N=int(input())
S=input()
D=defaultdict(list)
for i in range(N):
    D[S[i]].append(i)
ans=0
for k,v in D.items():
    if len(v)<2:continue
    for i in range(len(v)-1):
        for j in range(i+1,len(v)):
            if v[j]-v[i]>1 and v[j]<N-1:
                for a in range(v[i]+1,v[j]):
                    if S[a] in (S[v[i]],):continue
                    for b in range(v[j]+1,N-1):
                        if S[b] in (S[v[i]],S[a]):continue
                        for c in range(b+1,N):
                            if S[c] in (S[v[i]],S[a],S[b]):continue
                            #ans.add(f"{S[v[i]]}{S[e]}{S[v[j]]}{S[f]}{S[g]}")
                            ans+=1
print(ans)