#include<fstream.h>
#include<string.h>
#include<stdio.h>
ifstream f("litere.in");
ofstream g("litere.out");
int n,nr,i,gasit=1;
int main()
{
 char s[10001];
f>>n;
for(i=1;i<=n;i++)
  f>>s[i];
int j=n-1;
while(gasit)
{gasit=0;
 for(i=1;i<=j;i++)
  if(s[i]>s[i+1])
    {char x=s[i];
     s[i]=s[i+1];
     s[i+1]=x;gasit=1;nr++;}
   j--;
 }
g<<nr;
return 0;
}