#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int main()
{
    int n,i,ok,nr=0;
    char v[10003];
    in>>n;
    for(i=0;i<n;i++)
    {
        in>>v[i];
    }
    ok=1;
    while(ok)
    {
        ok=0;
        for(i=0;i<n-1;i++)
        {
            if(v[i]>v[i+1])
            {
                swap(v[i],v[i+1]);
                ok=1;
                nr++;
            }
        }
    }
    out<<nr;
    return 0;
}