#include <bits/stdc++.h>
using namespace std;
constexpr int N = 4005;
int n;
int cost[N][N];
array<int, 2> pos[N * N];
bool f[N][N];
int v;
bitset<N> al[N], ar[N], bl[N], br[N];
void upd(int l, int r) {
	if (f[l][r]) return;
	f[l][r] = 1;
	br[l].set(r);
	bl[r].set(l);
	if (l > 1 && r < n && !f[l - 1][r + 1] && cost[l - 1][r + 1] <= v) {
		upd(l - 1, r + 1);
	}
	auto sr = ar[l] & br[r + 1];
	for (int i = sr._Find_first(); i <= n; i = sr._Find_next(i)) {
		upd(l, i);
	}
	auto sl = al[r] & bl[l - 1];
	vector<int> ps;
	for (int i = sl._Find_first(); i <= n; i = sl._Find_next(i)) {
		ps.push_back(i);
	}
	for (int i : ps) {
		upd(i, r);
	}
}
int main() {
	cin.tie(0)->sync_with_stdio(0);
	cin >> n;
	for (int i = 1; i <= n; i++) {
		for (int j = i + 1; j <= n; j += 2) {
			cin >> cost[i][j];
			pos[cost[i][j]] = {i, j};
			ar[i].set(j);
			al[j].set(i);
		}
	}
	for (v = 1; v <= n * n / 4; v++) {
		auto [l, r] = pos[v];
		if (l + 1 == r || f[l + 1][r - 1]) upd(l, r);
		if (f[1][n]) {
			cout << v << "\n";
			return 0;
		}
	}
	return 0;
}