#include <bits/stdc++.h>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,x,sol,aib[200];
char ch;
void Update(int x)
{
	while (x <= 26)
	{
		aib[x]++;
		x += (x & (-x));
	}
}
int Query(int x)
{	
	int s = 0;
	while (x > 0)
	{
		s += aib[x];
		x -= (x & (-x));
	}
	return s;
}
int main()
{	
	fin >> n;
	for (int i = 0; i < n; i++)
	{
		fin >> ch;
		x = ch - 'a'+1;
		sol += i - Query(x);
		Update(x);
	}
	fout << sol;


	return 0;
}