#include <fstream>
#include <climits>
#include <algorithm>
#include <cstring>
using namespace std;

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

int main()
{
    
    char s[256],aux;
    int n,ok=1,nr=0;
    cin>>n;
    cin.get();
    cin.getline(s,256);
    while (ok==1){
        ok=0;
        for (int i=1; i<n;i++){
           if (s[i-1]>s[i]){
            nr ++;
            aux=s[i-1];
            s[i-1]=s[i];
            s[i]=aux;
            ok=1;
           }
        }
    }
    cout <<nr;
}