#include<stdio.h>   
  
FILE *f,*g;   
  
int n,i,inj,aux,j,nr;   
char a[10000];   
  
int main()   
{   
f=fopen("litere.in","rt");   
g=fopen("litere.out","wt");   
fscanf(f,"%d\n",&n);
for (i=1;i<=n;i++)   
    {
    fscanf(f,"%c",&a[i]);
    for(j=1;j<i;j++)
       if (a[i]<a[j])nr++;
    }
fprintf(g,"%d",nr);
fclose(g);
return 0;   
}