#include<bits/stdc++.h>
#define db double
using namespace std;
int n,pos[1000005],a[1000005];
struct BIT{
	int ct[1000005];
	void add(int p,int o){for(int i=p;i<=n;i+=(i&-i))ct[i]+=o;}
	int qry(int p){
		int res=0;
		for(int i=p;i;i&=(i-1))res+=ct[i];
		return res;
	}
}fwk;
int main(){
	scanf("%d",&n);
	db ans=(db)n;
	for(int i=1;i<=n;++i)scanf("%d",&a[i]),pos[a[i]]=i,fwk.add(i,1);
	int mn=n+1;
	for(int i=1;i<=n;++i){
		fwk.add(pos[i],-1);
		if(i==1)mn=pos[i];else mn=min(pos[i-1],pos[i]);
		ans+=(db)(fwk.qry(n)-fwk.qry(mn-1))*0.5000;
	}printf("%.10lf\n",ans);
	return 0;
}