#include <stdio.h>
int a[50],nr,i,j,n;
char c;

int main()
{
	FILE *in,*out;
	in=fopen("litere.in","r");
	out=fopen("litere.out","w");
	fscanf(in,"%d",&n);
	nr=0;
	fscanf(in,"\n");
	for (i=1;i<=n;i++)
	{
		fscanf(in,"%c",&c);
		for (j=0;j<=c-1-'a';j++)
			a[j]++;
		nr+=a[c-'a'];
	}
	fprintf(out,"%d\n",nr);
	fclose(in);
	fclose(out);
	return 0;
}