#include<fstream>
#define dmax 10010
#define dmax2 30
using namespace std;

int lg;
char s[dmax];
int v[dmax2];
long long sol;


void citire()
{
 ifstream fin("litere.in");
 
 fin>>lg; fin.get();
 fin.get(s,dmax);
 
 fin.close();
}


void solve()
{
 int i,j,nr;
	
 v[s[0] - 'a'] = 1;
 
 for (i=1; i<lg; i++)
	 {
	  nr=0;
	  
	  for (j=s[i]-'a'+1; j<=25; j++)
		 nr += v[j];
	 
	  v[s[i]-'a']++;
	  
	  sol += nr; 
	 }
}


void afisare()
{
 ofstream fout("litere.out");
 
 fout<<sol;
 
 fout.close();
}


int main()
{
	
 citire();
 solve();
 afisare();
	
 return 0;
}