import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

n = ni()
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):
                    if s[i] == s[k] and s[i] != s[j] and s[i] != s[l] and s[i] != s[m] and s[j] != s[l] and s[j] != s[m] and s[l] != s[m]:
                        ans += 1

print(ans)