from itertools import combinations
N = int(input())
S = input()

ans = 0
for a,b,c,d,e in combinations(range(N),5):
    if(len(set([S[a],S[b],S[c],S[d],S[e]])) != 4):continue
    if(S[a] != S[c]):continue
    ans += 1
print(ans)