/*litere*/

#include<fstream.h>
#include<string.h>

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

unsigned long contor;
int n;
char s[10005],cit[2];

int main()
{
	int i,j;
	fin>>n;
	fin.getline(cit,2);
	fin.getline(s,10005);

	n=strlen(s);

	for(i=n-1;i>=0;i--)
		for(j=i-1;j>=0;j--)
			if(s[i]<s[j])
				contor++;

	fout<<contor<<'\n';
	fout.close();
	return 0;
}