#include<bits/stdc++.h>
#define int long long
using namespace std;
#define fi first
#define se second
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define eb emplace_back
#define y1 yylyylyylyyl
#define pc __builtin_popcount
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef unsigned long long ull;
 
long long read() {
    long long res=0, w=1; char c=getchar();
    while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
    while(isdigit(c)) {res=res*10+c-48, c=getchar();}
    return res*w;
}

const int N=4009;
int n,x[N],y[N],mx,cur;
int val[N][N];
bitset<4009>L[2][N],R[2][N];
bool fin;

void extend(int x,int y) {
    if(x==1&&y==n) {fin=1; return;}
    //cout<<x<<" "<<y<<" "<<R[0][x][y]<<endl;
    R[0][x][y]=0, R[1][x][y]=1;
    L[0][y][x]=0, L[1][y][x]=1;
    auto b=R[0][x]&R[1][y+1];
    for(int p=b._Find_first();p<=n;p=b._Find_next(p)) {
        if(!(R[0][x][p]&R[1][y+1][p])) continue;
        extend(x,p);
    }
    b=L[0][y]&L[1][x-1];
    for(int p=b._Find_first();p<=n;p=b._Find_next(p)) {
        if(!(L[0][y][p]&L[1][x-1][p])) continue;
        extend(p,y);
    }
    int l0=x-1, r0=y+1;
    while(l0>=1&&r0<=n) {
        if(val[l0][r0]<=cur&&!R[1][l0][r0]) extend(l0,r0), l0--, r0++;
        else break;
    }
}

signed main() {
    n=read();
    rep(i,1,n) for(int j=i+1;j<=n;j+=2) {
        int p=read();
        x[p]=i, y[p]=j;
        mx=max(mx,p);
        val[x[p]][y[p]]=p;
    }
    rep(i,1,n) rep(j,i+1,n) R[0][i][j]=1, L[0][j][i]=1;
    rep(p,1,mx) {
        cur=p;
        //cout<<"ADD "<<p<<" "<<x[p]<<" "<<y[p]<<endl;
        if(x[p]+1==y[p]||R[1][x[p]+1][y[p]-1]) {
            int l0=x[p], r0=y[p];
            extend(l0,r0);
        }
        if(fin) return printf("%lld\n",p), 0;
    }
    return 0;
}