#include<iostream.h>
#include<fstream.h>
int main()
{
	ifstream f("litere.in");
	ofstream g("litere.out");
	int n,i,aux,j,nrinv=0;
	char s[10001];
	f>>n;
	f>>s;
	/*do
	{
		gata=1;
	for(i=0; i<n-1; i++)
	if(s[i]>s[i+1])
	{
		aux=s[i];
		s[i]=s[i+1];
		s[i+1]=aux;
		gata=0;
		nrinv++;
	}
	}
		while(!gata);*/
	for(i=0;i<n;i++)
	{
		aux=s[i];
			for(j=0;j<=i;j++)
				if(s[j]>aux) nrinv++;
	}
	
	g<<nrinv;
	return 0;
}