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

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