#include <iostream>
#include <fstream.h>

int main()
{
	ifstream f ("litere.in");
	ofstream g ("litere.out");
	
	char s[10005], aux;
	int n, i, contor = 0;
	bool ok = true;
	
	f >> n;
	f >> s;
	
	while(ok)
	{
		ok = false;
		for(i = 0; i < n - 1; i ++)
		{
			if(s[i] > s[i + 1])
			{
				contor ++;
				aux = s[i];
				s[i] = s[i + 1];
				s[i + 1] = aux;
				ok = true;
			}
		}
	}
	g << contor;
}