#include <stdio.h>         
int n,i=0,j,nr=0;         
char v[10000];         
int main()         
{freopen("litere.in","rt",stdin);         
scanf("%d", &n);         
gets(v);         
while (i<n)         
      {j=i+1;         
      while (j<n)         
       {if (v[i]>v[j]) ++nr;         
       ++j;         
      }         
     ++i;}         
freopen("litere.out","wt",stdout);         
printf("%d",nr);         
return 0;}