#include<stdio.h>
long n,i,j,k,l,rez,x[10001],y[10001];
char c,s[10001];
int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	scanf("%ld%c",&n,&c);
	gets(s);
	n--;
	for (i=0;i<=n;i++)
	{
		k=s[i]-96;
		for (j=1;j<=26;j++)
			if (k>j) x[j]++;
		rez+=x[k];
	}
	printf("%ld\n",rez);
	return 0;
}