#include<stdio.h>
int aux,sortat,n,i,x[10001];
long interschimbari;
/*
int partitie (int st,int dr)
{
int aux,m,i,j,pivot;
m=(st+dr)/2;
pivot=x[m];
i=st-1;
j=dr+1;
while(1)
	{
	do{i++;}while(x[i]<pivot);
	do{j--;}while(x[j]>pivot);
	if(i<j)
		{
		interschimbari++;
		aux=x[i];
		x[i]=x[j];
		x[j]=aux;
		}
	else return j;
	}
}
void qs (int st,int dr)
{
int p;
if(st<dr)
	{
	p=partitie(st,dr);
	qs(st,p);
	qs(p+1,dr);
	}
}
*/
int main ()
{
freopen("litere.in","r",stdin);
freopen("litere.out","w",stdout);
scanf("%d",&n);
scanf("%c",&x[0]);
for(i=1;i<=n;i++)
	scanf("%c",&x[i]);
do
{
sortat=1;
for(i=1;i<=n-1;i++)
	if(x[i]>x[i+1])
		{
		aux=x[i];
		x[i]=x[i+1];
		x[i+1]=aux;
		sortat=0;
		++interschimbari;
		}
}
while(sortat==0);

printf("%ld",interschimbari);
return 0;
}