#include <iostream>
#include <fstream>
using namespace std;
int fr[30];
char s[10001];
int main()
{
	ifstream in("litere.in");
	ofstream out("litere.out");
	int n, x;
	int ma = 0;
	int frmax = 0;
	in >> n;
	for (int i = 0;i < n;i++) {
		in >> s[i];
		fr[s[i] - 'a']++;
	}
	int contor = 0;
	for (int i = 0;i < n - 1;i++) {
		for (int j = i + 1;j < n;j++) {
			if (s[i] > s[j]) {
				contor++;
			}
		}
	}
	out << contor;
}