#include <fstream>

using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
char v[10001];
int n, p, nr, ok, i;
int main()
{
    cin>>n;
    cin>>v;
    nr=0;
    p=1;
    do
    {
        ok=1;
        for(i=0;i<n-p;i++)
            if(v[i]>v[i+1])
        {
            ok=0;
            nr++;
            swap(v[i],v[i+1]);
        }
        p++;
    }
    while(ok==0);
    cout<<nr;
    return 0;
}