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

int main()
{
    ifstream cin("litere.in");
    ofstream cout("litere.out");
    int cnt=0,n;
    cin >> n;
    string s;
    cin >> s;
    for(int i=0;i<s.size()-1;i++)
    {
        for(int j=i+1;j<s.size();j++)
        {
            if(s[i]>s[j])cnt++;
        }
    }
    cout << cnt;
    return 0;
}