#include <fstream>
#include <iostream>
#include <string>
#include <cmath>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");

int main()
{
	int n;
	long inter = 0;
	string sir;
	fin >> n;
	fin >> sir;
	bool ok = true;
	for (int i = 0; i < n - 1; i++)
	{
		for (int j = i + 1; j < n; j++)
		{
			if (sir[i] > sir[j])
			{
				char aux;
				aux = sir[i];
				sir[i] = sir[j];
				sir[j] = aux;
				inter++;
			}
		}
			
	}
		
	fout << inter;
	
	system("pause");
	return 0;
}