import itertools
import sys
input = sys.stdin.readline
N = int(input())
S = input().strip()
ans = 0
for l in itertools.combinations(range(N), 5):
    tmp = set()
    if S[l[0]]==S[l[2]]:
        for i in l:
            s = S[i]
            tmp.add(s)
        if len(tmp)==4:
            ans += 1
print(ans)