/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <fstream>
#include <cstring>
using namespace std;


ifstream cin("litere.in");
ofstream cout("litere.out");
int main()
{   int n, sol = 0, ok = 1; 
    
    char s[256];
    cin >> n;
    
    for (int i = 0; i < n; i++) {
        cin >> s[i];
     
    }
    do{ ok = 1;
        for (int i = 0; i < n - 1; i++) {
            if (s[i] > s[i + 1]) {
                sol ++;
                ok = 0;
                swap(s[i], s[i + 1]);
        }
        }
    } while (ok == 0);
    
     cout << sol;   
    
    return 0;
}