#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main() {
	ifstream f("litere.in");
	ofstream g("litere.out");
	
	int n, i, j, inv=0;
	string s;
	
	f>>n;
	f.get();
	getline(f,s);
	for(i=0; i<s.length()-1; i++) {
		for(j=i+1; j<s.length(); j++) {
			if(s[i]>s[j]) inv++;
		}
	}
	
	g<<inv<<"\n";
	
	
	f.close();
	g.close();
	return 0;
}