#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int n,aux,poz=0,i,j;
    char v[10000];
    f>>n;
    f>>v;
    for (i=1;i<=n;i++)
      for (j=1;j<=n;j++)
        if (v[j]>v[j+1])
         {
            aux=v[j];
            v[j]=v[j+1];
            v[j+1]=aux;
            ++poz;
         }
    g<<poz;
    return 0;
}