#include <fstream>

using namespace std;

ifstream in ("litere.in");
ofstream out ("litere.out");

char v[10001];

int main()
{
    int n,i,cnt=0,cnt1=0,j;
    char c;
    in>>n;
    in.get(c);
    for (i=0;i<n;i++)
        in.get(v[i]);
    bool ok=0;
    for (i=0;i<n-1;i++)
    {
        ok=0;
        for (j=0;j<n-i-1;j++)
           if (v[j]>v[j+1])
           cnt++,swap(v[j],v[j+1]),ok=1;
        if (ok==0)
            break;
    }
    out<<cnt;
    return 0;
}