#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
char s[100];
int n,i,j,mut,ok;
int main()
{
    fin>>n;
    fin>>s;
    while(ok!=1){
        ok=1;
        for(i=0;i<n-1;i++){
            if(s[i]>s[i+1]){
                swap(s[i],s[i+1]);
                ok=0; mut++;
                //fout<<s<<endl;
            }
        }
    }
    fout<<mut;
    return 0;
}