def func1(a,n):
for i in range(n):
a[i],a[i+n]=a[i+n],a[i]
return a
def func2(a,n):
i=1
for _ in range(n):
a[i],a[i-1]=a[i-1],a[i]
i+=2
return a
n=int(input())
l=list(map(int,input().split()))
a=l[:]
temp=l[:]
mn=10**9
for j in range(2):
ans=0
a=l[:]
while a[-1]!=2*n:
if j:
a=func2(a,n)
else:
a=func1(a,n)
ans+=1
j=not j
if a==sorted(l):
mn=min(mn,ans)
if mn==10**9:
print(-1)
else:
print(mn)
// #include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <iomanip>
#include <unordered_map>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <unordered_set>
#include <cstring>
#include <climits>
#include <algorithm>
using namespace std;
#define endl "\n"
#define int long long int
#define transform_to_upper(s) transform(s.begin(), s.end(),s.begin(),::toupper);
#define transform_to_lower(s) transform(s.begin(), s.end(),s.begin(),::tolower);
void fun(vector<int> & v){
int n=v.size();
for(int i=0;i<n;i+=2)swap(v[i],v[i+1]);
return ;
}
void fun2(vector<int> & v){
int n=v.size();
for(int i=0,j=n/2;j<n;i++,j++)swap(v[i],v[j]);
return ;
}
bool check(vector<int>a,vector<int> b){
for(int i=0;i<a.size();i++){
if(a[i]!=b[i])return false;
}
return true;
}
signed main(){
int n;
cin>>n;
n*=2;
vector<int> v(n);
for(int & val : v)cin>>val;
int ans1=-1,ans2=-1;
vector<int> one=v,two=v;
sort(v.begin(),v.end());
int operations=0;
while(operations<n){
if(check(v,one))break;
if(operations&1) fun(one);
else fun2(one);
operations++;
}
if(check(one,v)) ans1=operations;
operations=0;
while(operations<n){
if(check(v,two))break;
if(operations&1) fun2(two);
else fun(two);
operations++;
}
if(check(two,v)) ans2=operations;
if(ans1==-1||ans2==-1)cout<<max(ans1,ans2)<<endl;
else cout<<min(ans1,ans2)<<endl;
}1472A - Cards for Friends | 315A - Sereja and Bottles |
1697C - awoo's Favorite Problem | 165A - Supercentral Point |
1493A - Anti-knapsack | 1493B - Planet Lapituletti |
747B - Mammoth's Genome Decoding | 1591C - Minimize Distance |
1182B - Plus from Picture | 1674B - Dictionary |
1426C - Increase and Copy | 520C - DNA Alignment |
767A - Snacktower | 1365A - Matrix Game |
714B - Filya and Homework | 31A - Worms Evolution |
1691A - Beat The Odds | 433B - Kuriyama Mirai's Stones |
892A - Greed | 32A - Reconnaissance |
1236D - Alice and the Doll | 1207B - Square Filling |
1676D - X-Sum | 1679A - AvtoBus |
1549A - Gregor and Cryptography | 918C - The Monster |
4B - Before an Exam | 545B - Equidistant String |
1244C - The Football Season | 1696B - NIT Destroys the Universe |