#include <bits/stdc++.h>

using namespace std;

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

int n;
char s[10005];

void read()
{
    fin >> n;
    fin >> s;
}

void solve()
{
    int cont = 0;
    int i, j;
    for (i = 0; i < n-1; i++)
    for (j = 0; j < n-i-1; j++)
        if (s[j] > s[j+1])
        {
            swap(s[j], s[j+1]);
            cont++;
        }
    fout << cont;
}

int main()
{
    read();
    solve();
    return 0;
}