#include <fstream>
#define NMax 10000

int lg, max;
char a[NMax];

void citire();
void bsort();
int main()
{
	citire();
	bsort();
	return 0;
}
void bsort()
{
	int i, j;

	for (i=1; i<lg; i++)
		for (j=i-1; j>=0; j--)
			if ( a[i] < a[j] )
				max++;	

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