#include<stdio.h>

int i,j,ok,n,Hz[27],aux,k;
char a[10003];

int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);

	scanf("%d",&n);

	for(i=1;i<=n;i++)
	{
		scanf("%c",&a[i]);
		Hz[a[i]-'a']++;
	}

	for(i='a';i<='z';i++)
	{
		aux=Hz[i-'a'];
		for(j=1;j<=n;j++)
			if(i==a[j])
			{
				k+=j-1-aux-Hz[i-'a'];
				Hz[i-'a']--;
			}
	}

	printf("%d",k);

	return 0;
}