1 #include<bits/stdc++.h>
 2 #define maxn 3005
 3 using namespace std;
 4 int n,a[maxn],t[maxn];
 5 int msort(int l,int r){
 6     if(l==r) return 0;
 7     
 8     int m=l+r>>1;
 9     int t1=msort(l,m);
10     int t2=msort(m+1,r);
11     
12     int t3=0;
13     int i=l,j=m+1,k=l;
 
14     while(i<=m&&j<=r){
15         if(a[i]>a[j]){
16             t3+=m-i+1;
17             t[k++]=a[j++];
18         }
19         else{
20             t[k++]=a[i++];//本來就應該小於 
21         }
22     }
23     while(i<=m) t[k++]=a[i++];
24     while(j<=r) t[k++]=a[j++];
25
 
     
26     for(int p=l;p<=r;p++) a[p]=t[p];//調整
27     return t1+t2+t3; 
28 }
29 void init(){
30     scanf("%d",&n);
31     for(int i=1;i<=n;i++) scanf("%d",&a[i]);
32     int nd=msort(1,n);
33     if(nd&1){
34         printf("%lf",(double)(2*nd-1));
35     }
36     else printf("
 
%lf",(double)2*nd);
37 }
38 int main(){
39     init();
40     
41     return 0;
42 } 

CF351B Jeff and Furik