#include<stdio.h>
int v[27],i,n,j,s;
char x;
int main()
{
FILE*f=fopen("litere.in","r");
FILE*g=fopen("litere.out","w");

fscanf(f,"%d",&n);
fscanf(f,"%c",&x);
for (i=1;i<=n;i++)
     {
      fscanf(f,"%c",&x);
      v[(int)x-97]++;
      for (j=(int)x-96;j<=26;j++)
	    s+=v[j];
     }
fprintf (g,"%d",s);
fclose(f);
fclose(g);
return 0;
}