#include<stdio.h>
#include<string.h>
int n,i,sch;
long nr;
char x,a[10000];
int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	scanf("%d\n",&n);
	scanf("%s",&a);
	do
	{
		sch=0;
		for(i=0;i<n-1;++i)
			if(int(a[i])>int(a[i+1]))
							{
								x=a[i];
								a[i]=a[i+1];
								a[i+1]=x;
								sch=1;
								nr++;
							}
	}while(sch);

	printf("%ld\n",nr);
	return 0;
}