def solve():
    n = int(input())
    s = input()
    
    count = 0
    
    for i1 in range(n):
        for i2 in range(i1 + 1, n):
            for i3 in range(i2 + 1, n):
                for i4 in range(i3 + 1, n):
                    for i5 in range(i4 + 1, n):
                        pattern = [s[i1], s[i2], s[i3], s[i4], s[i5]]
                        
                        if pattern[0] == pattern[2] and len(set(pattern)) == 4:
                            count += 1
    
    print(count)

solve()