# include <stdio.h>

int k=0,i,n,j;
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]);

for (i=0;i<=n;i++)
{j=i;
while (a[j]<a[j-1])
{
aux=a[j];
a[j]=a[j-1];
a[j-1]=aux;
k++;
j--;
}
}




printf ("%ld",k);
fclose (stdout);
return 0;
}