#include <stdio.h>
int main(){
	FILE *f,*g;
	long i,j,n;
	int a[10002],l[27];
	char ch;
	f=fopen("litere.in","r");
	g=fopen("litere.out","w");
	fscanf(f,"%ld\n",&n);
	long nr=0;
	for(i=0;i<=26;i++) l[i]=0;
	for(i=1;i<=n;i++){
		fscanf(f,"%c",&ch);
		a[i]=ch-96;
		l[a[i]]++;	
	}
	for(i=1;i<=n;i++){
		for(j=1;j<a[i];j++)
			nr+=l[j];
		l[a[i]]--;
	}
	fprintf(g,"%ld\n",nr);
	fclose(f);
	fclose(g);
	return 0;
}