import sys

sys.setrecursionlimit(10 ** 9)
n = int(input())
s = [v for v in input()]

lis = []
def dfs(l: list[str], idx: int):
    if len(l) == 5:
        lis.append(l)
        return
    for i in range(idx + 1, n):
        if len(l) == 2 and s[i] != l[0]:
            continue
        
        if len(l) == 1 or len(l) > 2:
            if s[i] in l:
                continue
        dfs(l + [s[i]], i)

for i in range(n):
    dfs([s[i]], i)

print(len(lis))