#include <stdio.h>         
int n,nr=0;
char v[10000];         
void sortare_insertie(char a[], int length)
{
int i,j;
for (i=0;i<length;i++)
{
char v1=a[i];
for (j=i-1;j>=0;j--)
{
if (a[j]<=v1) break;
a[j+1]=a[j];
nr++;
}
a[j+1]=v1;
}
}

int main()
{freopen("litere.in","rt",stdin);         
scanf("%d\n", &n);         
gets(v);
sortare_insertie(v,n);
freopen("litere.out","wt",stdout);
printf("%d",nr);
return 0;}