using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(int n) => Enumerable.Repeat(0, n).Select(_ => NList).ToArray();
    static void Main()
    {
        var n = NN;
        var s = ReadLine();
        var set = new HashSet<long>();
        for (var i = 0; i + 1 < s.Length; ++i)
        {
            var key = 0L;
            if (s[i] == 'A') key += i + 1;
            if (s[i + 1] == 'A')
            {
                key = key * 1_000_000_000L + i + 2;
            }
            set.Add(key);
        }
        WriteLine(set.Count);
    }
}