N = int(input())
S = input()
def generate_subsequences(s, length):
    result = []
    
    def backtrack(start, current):
        if len(current) == length:
            result.append(current)
            return
        
        for i in range(start, len(s)):
            backtrack(i + 1, current + s[i])
    
    backtrack(0, "")
    return result

ans = 0
subsequences = generate_subsequences(S, 5)
# print(sorted(subsequences))
for i in subsequences:
    if i[0] == i[2]:
        if len(set(i)) == 4:
            ans += 1

print(ans)