#include <stdio.h>
#include <string.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
int ok,ap,n;
char c[10000],z;
int main(){
 fscanf(f,"%d\n",&n);
 fscanf(f,"%s",&c);
 do{
  ok=1;
  for(int i=0;i<strlen(c)-1 && ok;i++){
   if(c[i]>c[i+1]){
    ok=0;
    z=c[i];
    c[i]=c[i+1];
    c[i+1]=z;
    ap++;
   }
  }
 }while(!ok);
 fprintf(g,"%d",ap);
return 0;
}