#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("litere.in");
ofstream fout("litere.out");

int main()
{
    ios_base :: sync_with_stdio(false);
    fin.tie(nullptr), fout.tie(nullptr);

    short cnt = 0, n;
    string s;
    fin>>n>>s;

    for (short i = 0; i < n-1; i++) {
        char minimum = s[i];
        short position = i;

        for (short j = i+1; j < n; j++)
            if (s[j] < minimum)
                minimum = s[j], position = j;
        
        for (short j = position; j > i; j--)
            swap(s[j], s[j-1]), cnt++;
    }

    fout<<cnt;
    return 0;
}