#include<iostream>
#include<fstream>
#include<cstring>
using namespace std;
int main()
{
	ifstream fin("litere.in");
	ofstream fout("litere.out");
	char a[10001];
	int i,j,n,rez,sortat;
	rez=0;
	fin>>n;
	fin.get();
	fin.get(a,10001);
	sortat=0;
	while(!sortat)
	{
		sortat=1;
					for(i=0;i<n-1;i++)
	if(a[i]>a[i+1])
	{
		int aux=a[i];
		a[i]=a[i+1];
		a[i+1]=aux;
		sortat=0;
		rez++;
	}
	//sortat=0;
	}
	fout<<rez;
	return 0;
}