#include<stdio.h>
long k,n,i,j,o;
char aux,a[1001];
int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	scanf("%ld",&n);
	for(i=0;i<=n;i++)
		scanf("%c",&a[i]);
	do
	{
		o=0;
		for(i=1;i<n;i++)
			if(a[i]>a[i+1])
				{
					aux=a[i];
					a[i]=a[i+1];
					a[i+1]=aux;
					k++;
				}
		for(i=1;i<n;i++)
			if(a[i]>a[i+1])
				{
					o=1;
					break;
				}
	}
	while(o==1);
	printf("%ld\n",k);
	return 0;
}