#include<stdio.h>
#include<string.h>

long n,j,c,i,bubble;

char lit[10001],aux;

int main()

{

freopen("litere.in","r",stdin);
freopen("litere.out","w",stdout);

scanf("%ld \n",  &n);

for (i=1;i<=n;i++)

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


while (!bubble)   //buble sort :D:D

{
bubble=1;

for (i=1;i<n;i++)



if ( lit[i]>lit[i+1])


{


c++; //contor

bubble=0;

aux=lit[i];  //interschimbam :D:D   a-b  b-a :D:D

lit[i]=lit[i+1];

lit[i+1]=aux;



}







}




printf("%ld", c);





return 0;

}