#include <stdio.h>

int main () {
	long n,nr=0,mut=1,i; char a[10010],x;
	freopen ("litere.in","r",stdin);
	freopen ("litere.out","w",stdout);
	scanf ("%d",&n); scanf ("%c",&x);
	for (i=0; i<n; i++) scanf ("%c",&a[i]);
	while (mut) {
		mut=0;
		for (i=0; i<n-1; i++)
			if (a[i]>a[i+1]) {
				nr++;
				x=a[i]; a[i]=a[i+1]; a[i+1]=x;
				mut=1;
			}
	}
	printf ("%ld\n",nr);
	return 0;
}