#include <fstream>
using namespace std;

#define nmax 10001
int n;
char sir[nmax];
long inv;

inline void citire()
{
	ifstream in("litere.in");
	in>>n;
	in>>sir;
}

inline void afisare()
{
	ofstream out("litere.out");
	out<<inv;
}

void rez()
{
	int i,j;
	for(i=0;i<n;i++)
		for(j=i+1;j<n;j++)
			if(sir[i]>sir[j])
				inv++;
	afisare();
}

int main()
{
	citire();
	rez();
	return 0;
}