#include<iostream>
#include<stdio.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
int a[10001];
int main()
{
	int n,i,j,op=0;
	char c[10001];
	int t=1,ul;
	fscanf(f,"%d %s",&n,&c);
        ul=n-1;
	for(i=97;i<=122;i++)
	{
	 int aux=0;
	 for(j=0;j<n;j++)
	 {
	  if(i<(int)c[j]) aux++;
	  if(i==(int)c[j]) a[j]=aux;
	 }
        }
	for(i=0;i<n;i++)
         op+=a[i];
	fprintf(g,"%d\n",op);
	return 0;
}