#include<cstdio>
#include<cstring>
#include<iostream>
#define DMAX 32768
using namespace std;
char v[DMAX],aux[DMAX];int s;
void sortare(int l,int r)
{
	if(l==r)return;
	int m=(l+r)>>1,i=l,j=m+1,k=l;
	sortare(l,m);sortare(m+1,r);
	while(i<=m||j<=r)
		if((v[i]<v[j]&&i<=m)||j>r)
			aux[k++]=v[i++];
		else
			aux[k++]=v[j++];
	for(s+=r-l;l<=r;l++)
		v[l]=aux[l];
}
int main()
{
	freopen("litere.in","r",stdin);freopen("litere.out","w",stdout);
	int n;
	scanf("%d%s",&n,v);strcpy(v+1,v);sortare(1,n);printf("%d",s-1);
}