#include<iostream.h>
#include<string.h>
#include<fstream.h>
int i,n,k;
char a[10000],c;
fstream f("litere.in",ios::in),g("litere.out",ios::out);
void main()
{f>>n;f.get();
f.get(a,10000);
i=1;
while(i<n)
 if(a[i]<a[i-1])
  { k++;
   c=a[i-1];
   a[i-1]=a[i];
   a[i]=c;
   i--;
   }
 else i++;
g<<k;
}