#include <stdio.h>

using namespace std;

FILE *f,*s;

char l;
int n,i,j,frecv[30];
long long int rez;

int main()
{
	f=fopen("litere.in","r");
	s=fopen("litere.out","w");
	
	fscanf(f,"%d\n",&n);
	
	for(i=1;i<=n;i++)
	{
		fscanf(f,"%c",&l);
		
		for(j=1;j<=26;j++)
		{
			if(l-96<j)
				rez+=frecv[j];
		}
		
		frecv[l-96]++;
	}	
	
	fprintf(s,"%lld",rez);
	
	
	fclose(s);
	
	return 0;
}