#include <fstream>
using namespace std;

ifstream fin("litere.in");
ofstream fout("litere.out");

char a[10001];
int n;

int main()
{
	fin >> n;
	int pp = 0;
	fin.get();
	fin.getline(a, 10001 );
	bool sortat = false;
	
	while ( !sortat )
	{
		sortat = true;
		for ( int i = 0; i < n-1; i++ )
			if ( a[i] > a[i+1] )
			{
				int aux;
				aux = a[i+1];
				a[i+1] = a[i];
				a[i] = aux;
				sortat = false;
				pp++;
			}
	}
	
	
	
	fout << pp << '\n';
	fin.close();
	fout.close();
	return 0;
}