#include<stdio.h>
int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	int n,num=0,sortat,i;
	char s[10001],aux;
	
	scanf("%d\n",&n);
	gets(s);
	do
	{
		sortat=1;
		for(i=0;i<n-1;i++)
			if(s[i]>s[i+1])
			{
				num++;
				aux=s[i];
				s[i]=s[i+1];
				s[i+1]=aux;
				sortat=0;
			}
	}while(sortat==0);
	printf("%d",num);
	return 0;
}