#include <fstream>
#define NMax 10000

int lg, max;
char a[NMax];

void citire();
void bsort();
int main()
{
	citire();
	bsort();
	return 0;
}
void bsort()
{
	int ok, i;
	char aux;
	
	do 
	{
		ok = 0;
		for (i=0; i<lg-1;i++)
			if ( a[i] > a[i+1] )
			{
				aux = a[i];
				a[i] = a[i+1];
				a[i+1] = aux;
				ok = 1;
				max++;
			}
	} while(ok);

	std::ofstream g("litere.out");
	g << max << '\n';
}
void citire()
{
	std::ifstream f("litere.in");
	f >> lg >> a ;
	f.close();
}