# include <stdio.h>

int k=0,i,n,ord;
char a[1000],aux;
int main ()
{
freopen ("litere.in","r",stdin);
freopen ("litere.out","w",stdout);


scanf ("%ld",&n);
for (i=0;i<=n;i++)

scanf ("%c",&a[i]);


ord=0;
while (ord==0)
{
ord=1;
for (i=0;i<=n-1;i++)
if (a[i]>a[i+1])
{
aux=a[i];
a[i]=a[i+1];
a[i+1]=aux;
ord=0;
k++;
}
}
printf ("%ld",k);
fclose (stdout);
return 0;
}