#include <fstream>
#include <algorithm>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,s[10001];
long long sol;
char v[10001];
int main()
{
    fin>>n;
    fin>>v;
    for(int i=0;i<=n-1;i++)
    {
        s[i]=v[i];
    }
    int nr;
    while(nr!=0)
    {
        nr=0;
        for(int i=1; i<=n-1; i++)
        {
            if(s[i-1]>s[i])
            {
                char aux=s[i-1];
                s[i-1]=s[i];
                s[i]=aux;
                sol++;
                nr++;
            }
        }

    }

    fout<<sol;
    return 0;
}