#include<bits/stdc++.h>
using namespace std;

ifstream in("litere.in");
ofstream out("litere.out");

vector<char>v;
int n, k=0, rasp=0;
bool lp=1;

int main(){
	in>>n;
	v.resize(n);
	for(int i=0;i<n;i++){
		in>>v[i];
	}
	while(lp){
		lp=0;
		for(int i=k;i<n-1;i++){
			if(v[i]-'a'>v[i+1]-'a'){
				swap(v[i],v[i+1]);
				i-=2;
				k=i;
				rasp++;
				lp=1;
			}    
		}
	}
	out<<rasp;
}