#include <iostream>
#include <fstream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
char T[10005];
int main()
{
    int n;
    in>>n;
    in.getline(T,0);
    in.getline(T,10000);
    int nr=0;
    int ok=0;
    int v[n+1];
    for(int i=0;i<n;i++)
        v[i+1]=(int)T[i];
    while(ok==0)
    {
        ok=1;
        for(int i=1;i<=n-1;i++)
        {
            if(v[i]>v[i+1])
            {
                nr++;
                ok=0;
                swap(v[i],v[i+1]);
            }
        }
    }
    out<<nr;
    return 0;
}