#include <bits/stdc++.h>
using namespace std;
const int maxn = 4005;
template <typename T>
void read(T &x) {
	T sgn = 1;
	char ch = getchar();
	for (; !isdigit(ch); ch = getchar()) if (ch == '-') sgn = -1;
	for (x = 0; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
	x *= sgn;
}
int n, c[maxn][maxn];
pair<int, int> pos[4010005];
bitset<maxn> f[maxn], g[maxn];
void ins(int x, int y) {
	f[x].set(y); g[y].set(x);
	if (x > 1 && y < n && c[x][y] > c[x - 1][y + 1])
		ins(x - 1, y + 1);
	for (int now = (f[y + 1] & (~f[x]))._Find_next(y); now <= n; now = (f[y + 1] & (~f[x]))._Find_next(now)) {
		ins(x, now);
	}
	for (int now = (g[x - 1] & (~g[y]))._Find_next(0); now < x; now = (g[x - 1] & (~g[y]))._Find_next(now)) {
		ins(now, y); 
	}
}
int main() {
//	freopen("deleting.in", "r", stdin); freopen("deleting.out", "w", stdout);
	read(n);
	for (int i = 1; i < n; i++) {
		for (int j = i + 1; j <= n; j += 2) {
			read(c[i][j]);
			pos[c[i][j]] = make_pair(i, j);
		}
	}
	for (int i = 1; i <= (n / 2) * (n / 2); i++) {
		int l = pos[i].first, r = pos[i].second;
		if ((l + 1 == r || f[l + 1].test(r - 1)) && !f[l].test(r)) ins(l, r);
		if (f[1].test(n)) {
			printf("%d\n", i);
			break;
		}
	}
	return 0;
}