#include <stdio.h>
char v[1000];
int n,i,f,p,a;
FILE *in,*o;
void main()
{
in=fopen("litere.in","r");
o=fopen("litere.out","w");
fscanf(in,"%d%c",&n,&f);
for (i=1;i<=n;i++)
 fscanf(in,"%c",&v[i]);
f=0;
while (f==0)
{
f=1;
for (i=1;i<n;i++)
 if (v[i]>v[i+1])
  {
  a=v[i];
  v[i]=v[i+1];
  v[i+1]=v[i];
  f=0;
  p++;
  }
}
fprintf(o,"%d",p);
fclose(in);
fclose(o);
}