#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;

ifstream f("litere.in");
ofstream g("litere.out");

char sir[10001];
int n, i, j, rasp, i2;
int main()
{
    f >> n; // n = strlen(sir)
    f >> sir;
    /*for(i = 0; i < n - 1; i++)
    {
        for(j = i + 1; j < n; j++)
        {
            if(sir[i] > sir[j])
            {
                cout << "rasp = " << rasp +1 << '\n' << "i = " << i << "; j = " << j << '\n' << "sir[i] = " << sir[i] << "; sir[j] = " << sir[j] << '\n' << '\n' << '\n';
                swap(sir[i],sir[j]);
                rasp++;
            }
        }
    }*/
    for(i = 0; i < n - 1; i++)
    {
        i2 = i;
        for(j = i + 1; j > 0; j--)
        {
            if(sir[j] < sir[i2])
            {
                swap(sir[j], sir[i2]);
                rasp++;
            }
            i2--;
        }
    }
    g << rasp;
    //cout << '\n' << '\n' << sir;
    return 0;
}