#include <fstream>
#include <queue>
#include <iostream>
using namespace std;
int n,ct;
bool x;
string s;
int main()
{
    ifstream f ("litere.in");
    ofstream g ("litere.out");
    f>>n;
    f>>s;
    for (int i=0;i<n;i++)
    {
        for (int j=i;j<n;j++)
        {
            if (s[j]>s[j+1])
            {
                ct++;
                swap(s[j],s[j+1]);
            }
        }
    }
    g<<ct;
}