using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var s = Console.ReadLine().ToList();

        var count = 0;
        var times = 0;

        for (int i = 0; i < s.Count; i++)
        {
            if (s[i] == 'A' || s[i] == 'C' || s[i] == 'G' || s[i] == 'T') count++;
        }


        while (count != 0)
        {
            if (s[count - 1] == 'A' || s[count - 1] == 'C' || s[count - 1] == 'G' || s[count - 1] == 'T')
            {
                s.RemoveAt(count - 1);
                times++;
                count--;
            }
            else
            {
                s.RemoveAt(count - 1);
                times++;
            }
        }

        Console.WriteLine(times);
    }
}