#include<fstream>
using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");
int n,nr,ok;
char x[10002],aux;
int main()
{
    f>>n>>x;
    do
    {   ok=0;
        for(int i=1;i<n-1;i++)
            if(x[i]>x[i+1])
                {   aux=x[i];
                    x[i]=x[i+1];
                    x[i+1]=aux;
                    ok=1;
                    nr++;
                }
    }
    while(ok==1);
    g<<nr;
	g.close();
    return 0;
}