#include <fstream.h>
int main(){
int n,i,g=1,m=0,k,j;
char a[10000];
ifstream fin("litere.in");
ofstream fout("litere.out");
fin>>n;
for (i=1;i<=n;i++) fin>>a[i];

for (i=97;i<=122;i++)
for (j=g;j<=n;j++)
if (a[j]==i){
	m=m+j-g;
	g=g+1;
	for (k=j;k>=g;k--) a[k]=a[k-1];
	}

	fout<<m;
	fout.close();




return 0;
}