#include<stdio.h>

int i,j,n,s,sol[10000];
char a[10000];

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

	scanf("%d",&n);
	scanf("%s",a);

	for(i=1;i<n;i++)
		{
		s=0;
		for(j=0;j<i;j++)
			if(a[i]<a[j])
				s++;
		sol[i]=s;
		}
	s=0;
	for(i=1;i<=n;i++)
		s+=sol[i];

	printf("%d",s);
	return 0;
}