//Bismillah Hir Rehmanir Rahim
//Allah knows best
#include<bits/stdc++.h>
using namespace std;
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <bitset>
#define endl "\n"
#define mini -10000000000000000
#define ios ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define f(i, a, n) for( i=a; i<n;i++)
#define ll long long
#define pi 3.141592653589793
#define vi              vector<int>
#define si              set<int>
#define pb              push_back
#define mp              make_pair
#define mod             1000000000000000000
#define rr              return 0
#define ff              first
#define in              insert
#define ss              second
#define all(a) a.begin(), a.end()
typedef pair<int, int> pii;
#define setbits(x)      builtin_popcountll(x)
#define zrbits(x)       builtin_ctzll(x)
#define deb(x)          cout << #x << " = " << x << endl
#define set_bit(x, idx) x = x|1LL<<idx
#define check_bit(x, idx) min(x&(1LL<<idx),1LL)
#define toggle_bit(x, idx) x = x^(1LL<<idx)
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using    namespace __gnu_pbds;
#define multi_ordered_set       tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
typedef tree<int, null_type, greater<int>, rb_tree_tag, tree_order_statistics_node_update> rordered_set;
#ifdef DEBUG
#define ok cerr << __LINE__ <<"is done "<<endl;
#else
#define ok 
#endif
ll ncr[1001][1001];
void calcncr()
{
  for(int i = 0; i <= 1000; i++)
  {
    ncr[i][0] = 1;
  }
  for(int i = 1; i <= 1000; i++)
  {
    for(int j = 1; j <= 1000; j++)
    {
      ncr[i][j] = (ncr[i-1][j-1] + ncr[i-1][j])%mod;
    }
  }
}
int main()
{
    ios;
    #ifdef DEBUG
    freopen("in", "r", stdin);
    #endif 
    ll i,j,n,m,k;
	ll t;
	t=1;
    calcncr();
	//cin>>t;
	while(t--)
	{
        ll l;
      cin>>l;
      cout<<ncr[l-1][l-12]<<endl;
	}
    rr;
}
#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
#define DEBUG
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = (1<<30)-1;
const ll linf = 1LL<<61;
const int MAX = 510000;
int dy[8] = {0,1,0,-1,1,-1,-1,1};
int dx[8] = {-1,0,1,0,1,-1,1,-1};
const double pi = acos(-1);
const double eps = 1e-9;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    int sz = a.size();
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr;
        sz--;
        if(sz) cout << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
const int mod = 1e9 + 7;
//const int mod = 998244353;

struct UnionFind{
    vl p;
    vl rank;
    vl cnt;

    UnionFind(ll n){
        rank.resize(n,0);
        p.resize(n,0);
        cnt.resize(n,0);
        rep(i,n){
            p[i] = i;
            rank[i] = 0;
            cnt[i] = 1;
        }
    }

    ll find(ll x){
        if(x != p[x]) p[x] = find(p[x]);
        return p[x];
    }

    bool same(ll x, ll y){
        return find(x) == find(y);
    }

    void unite(ll x, ll y){
        x = find(x);
        y = find(y);
        if(x == y) return;
        if(rank[x] > rank[y]){
            p[y] = x;
            cnt[x] += cnt[y];
        }else{
            p[x] = y;
            cnt[y] += cnt[x];
            if(rank[x] == rank[y]) rank[y]++;
        }
    }

    ll size(ll x){
        return cnt[find(x)];
    }
};

UnionFind uf(202020);

int main(){
    int n; cin >> n;
    vl a(n); rep(i,n) cin >> a[i];
    int ans = 0;
    rep(i,n/2){
        if(uf.same(a[i],a[n-i-1])) continue;
        uf.unite(a[i],a[n-i-1]);
        ans++;
    }
    cout << ans << endl;
}