int n = int.Parse(Console.ReadLine());
string s = Console.ReadLine();
int count = 0;

for (int i = 0; i < n; i++)
{
    for (int j = i + 1; j < n; j++)
    {
        for (int k = j + 1; k < n; k++)
        {
            for (int l = k + 1; l < n; l++)
            {
                for (int m = l + 1; m < n; m++)
                {
                    if (s[i] == s[k])
                    {
                        if (!(s[j] == s[i] || s[j] == s[l] || s[j] == s[m] || s[k] == s[l] || s[k] == s[m] || s[l] == s[m]))
                        {
                            count++;
                        }
                    }
                }
            }
        }
    }
}

Console.WriteLine(count);