#include<fstream.h>
int main()
{
	int v[10001],n,i,ok,aux,k=0;
	char c;
	ifstream f("litere.in");
	ofstream g("litere.out");
	f>>n;
	for (i=1;i<=n;i++)
	{
		f>>c;
		v[i]=c-'a'+1;
	}
	do
	{
		ok=1;
		for (i=1;i<=n-1;i++)
			if (v[i]>v[i+1])
			{
				aux=v[i];
				v[i]=v[i+1];
				v[i+1]=aux;
				k++;
				ok=0;
			}
	}
	while (ok==0);
	g<<k;
	return 0;
}