#include<stdio.h>

FILE *f,*g;

long n,i,inj,aux,j,nr,a[10000];
char c;

int main()
{
f=fopen("litere.in","rt");
g=fopen("litere.out","wt");
fscanf(f,"%ld\n",&n);
for (i=1;i<=n;i++)
    {
    fscanf(f,"%c",&c);
    a[i]=c-'a'+1;
    }
for (i=1;i<=n;i++)
    for(j=1;j<i;j++)
       if (a[i]<a[j])nr++;
fprintf(g,"%d",nr);
fclose(f);
fclose(g);
return 0;
}