#include<iostream>
#include<stdio.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
int a[10001];
int main()
{
	int n,i,j,op=0;
	char c[10001];
	int t=1,ul;
	fscanf(f,"%d %s",&n,&c);
        ul=n-1;
	for(i=0;i<n;i++)
	{
		for(j=i-1;j>=0;j--)
		if(c[i]<c[j]) a[i]++;
	}
	for(i=0;i<n;i++)
         op+=a[i];
	fprintf(g,"%d\n",op);
	return 0;
}