#include<stdio.h>

#define N 10000

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