#include <stdio.h>
char a[10005];
int v[27];
int n,k;
void solve ()
{
    int i,j;
    scanf ("%d\n",&n);
    gets (a);
	for (i=0; i<n; ++i)
    {
        for (j=1; j<=26; ++j)
			if (j+'a'-1>a[i])
				k+=v[j];
		++v[a[i]-'a'+1];
    }
    printf ("%d",k);
}
int main ()
{
    freopen("litere.in","r",stdin);   
    freopen("litere.out","w",stdout); 
    solve ();
    return 0;
}