#include<stdio.h>

long long int m,cont,N,i;
char c[10000],aux;

int main()
{

FILE*in=fopen("litere.in","r");
FILE*out=fopen("litere.out","w");
fscanf(in,"%lld",&N);
for(i=1;i<=N;i++)
 fscanf(in,"%c",&c[i]);
m=1;
while(m)
 {
  m=0;
  for(i=2;i<=N;i++)
  {
   if(int(c[i+1])<int(c[i]))
    {
     aux=c[i]; c[i]=c[i+1]; c[i+1]=aux;
     m=1; cont++;
    }
  }

 }

fprintf(out,"%lld",cont);

fcloseall();
return 0;
}