Problem:
Score : 1300 points

Problem Statement

We have a pyramid with N steps, built with blocks.
The steps are numbered 1 through N from top to bottom.
For each 1≤i≤N, step i consists of 2i-1 blocks aligned horizontally.
The pyramid is built so that the blocks at the centers of the steps are aligned vertically.

A pyramid with N=4 steps

Snuke wrote a permutation of (1, 2, ..., 2N-1) into the blocks of step N.
Then, he wrote integers into all remaining blocks, under the following rule:

The integer written into a block b must be equal to the median of the three integers written into the three blocks directly under b, or to the lower left or lower right of b.

Writing integers into the blocks

Afterwards, he erased all integers written into the blocks.
Now, he only remembers that the permutation written into the blocks of step N was (a_1, a_2, ..., a_{2N-1}).

Find the integer written into the block of step 1.

Constraints

2≤N≤10^5

(a_1, a_2, ..., a_{2N-1}) is a permutation of (1, 2, ..., 2N-1).

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 ... a_{2N-1}

Output

Print the integer written into the block of step 1.

Sample Input 1

4
1 6 3 7 4 5 2

Sample Output 1

4

This case corresponds to the figure in the problem statement.

Sample Input 2

2
1 2 3

Sample Output 2

2

Solution in C++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef pair<int,int> ii;
typedef pair<ii,int> iii;
#define REP(i,n) for(int i=0;i<n;i++)
#define REP1(i,n) for(int i=1;i<=n;i++)
#define RST(i,n) memset(i,n,sizeof i)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(),a.end()
#define X first
#define Y second
#define eb emplace_back
#ifdef cold66
#define debug(...) do{\
    fprintf(stderr,"LINE %d: (%s) = ",__LINE__,#__VA_ARGS__);\
    _do(__VA_ARGS__);\
}while(0)
template<typename T>void _do(T &&_x){cerr<<_x<<endl;}
template<typename T,typename ...S> void _do(T &&_x,S &&..._t){cerr<<_x<<", ";_do(_t...);}
template<typename _a,typename _b> ostream& operator << (ostream &_s,const pair<_a,_b> &_p){return _s<<"("<<_p.X<<","<<_p.Y<<")";}
template<typename It> ostream& _OUTC(ostream &_s,It _ita,It _itb)
{
    _s<<"{";
    for(It _it=_ita;_it!=_itb;_it++)
    {
        _s<<(_it==_ita?"":",")<<*_it;
    }
    _s<<"}";
    return _s;
}
template<typename _a> ostream &operator << (ostream &_s,vector<_a> &_c){return _OUTC(_s,ALL(_c));}
template<typename _a> ostream &operator << (ostream &_s,set<_a> &_c){return _OUTC(_s,ALL(_c));}
template<typename _a,typename _b> ostream &operator << (ostream &_s,map<_a,_b> &_c){return _OUTC(_s,ALL(_c));}
template<typename _t> void pary(_t _a,_t _b){_OUTC(cerr,_a,_b);cerr<<endl;}
#define IOS()
#else
#define debug(...)
#define pary(...)
#define endl '\n'
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0);
#endif // cold66
//}
template<class T> inline bool chkmax(T &a, const T &b) { return b > a ? a = b, true : false; }
template<class T> inline bool chkmin(T &a, const T &b) { return b < a ? a = b, true : false; }

const ll MAXn=2e5+5,MAXlg=__lg(MAXn)+2;
const ll MOD=1000000007;
const ll INF=0x3f3f3f3f;

int n;
int d[MAXn];
bool chk(int x){
    vector<int> tmp;
    for (int i=0;i<2*n-1;++i) {
        int tp = 0;
        if (d[i] >= x) tp = 1;
        else tp = 0;
        tmp.eb(tp);
    }
    debug(x,tmp);
    if ((tmp[n-2] == 1 && tmp[n-1] == 0 && tmp[n] == 1) || (tmp[n-2] == 0 && tmp[n-1] == 1 && tmp[n] == 0)) {
        for (int i=1;i<=2*n;++i) {
            debug(n-i-1);
            if (n-1-i < 0) {
                return tmp[0];
            }
            if (tmp[n-1-i] != tmp[n-1+i]) {
                if (i&1) return tmp[n-1];
                return !tmp[n-1];
            }
        }
    }
    else {
        if (tmp[n-2] + tmp[n-1] + tmp[n] >= 2) return 1;
        return 0;
    }
    return 0;
}
int main(){
    IOS();
    cin >> n;
    for (int i=0;i<2*n-1;++i) {
        cin >> d[i];
    }
    int l = 2, r = n*2-1;
    while (l != r-1) {
        int mid = (l+r)>>1;
        if (chk(mid)) l = mid; 
        else r = mid;
    }
    cout << l << endl;
}