//use itertools::Itertools;
use std::cmp;
use std::collections::BTreeMap;
use std::collections::BTreeSet;
use std::collections::BinaryHeap;
use std::collections::HashMap;
use std::collections::HashSet;
use std::collections::VecDeque;
use std::io::Read;
use std::usize::MAX;

macro_rules! input {(source = $s:expr, $($r:tt)*) => {let mut iter = $s.split_whitespace();let mut next = || { iter.next().unwrap() };input_inner!{next, $($r)*}};($($r:tt)*) => {let stdin = std::io::stdin();let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));let mut next = move || -> String{bytes.by_ref().map(|r|r.unwrap() as char).skip_while(|c|c.is_whitespace()).take_while(|c|!c.is_whitespace()).collect()};input_inner!{next, $($r)*}};}
macro_rules! input_inner {($next:expr) => {};($next:expr, ) => {};($next:expr, $var:ident : $t:tt $($r:tt)*) => {let $var = read_value!($next, $t);input_inner!{$next $($r)*}};}
macro_rules! read_value {($next:expr, ( $($t:tt),* )) => {( $(read_value!($next, $t)),* )};($next:expr, [ $t:tt ; $len:expr ]) => {(0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()};($next:expr, chars) => {read_value!($next, String).chars().collect::<Vec<char>>()};($next:expr, usize1) => {read_value!($next, usize) - 1};($next:expr, [ $t:tt ]) => {{let len = read_value!($next, usize);(0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()}};($next:expr, $t:ty) => {$next().parse::<$t>().expect("Parse error")};}

fn solve() {
    input! {
        n: usize,
        a: [[usize1;n-1];n]
    }
    let mut ans = 0;

    let mut adj_list: HashMap<(usize, usize), Vec<(usize, usize)>> = HashMap::new();
    let mut deg: HashMap<(usize, usize), usize> = HashMap::new();

    let mut edges = Vec::new();

    for i in 0..n {
        for j in i + 1..n {
            adj_list.entry((i, j)).or_insert_with(Vec::new);
            deg.entry((i, j)).or_insert(0);
        }
    }

    for i in 0..n {
        for now in 0..n - 2 {
            let next = now + 1;

            let now_node = (cmp::min(i, a[i][now]), cmp::max(i, a[i][now]));
            let next_node = (cmp::min(i, a[i][next]), cmp::max(i, a[i][next]));
            edges.push((next_node, now_node));

            let deg_count = deg.entry(next_node).or_insert(0);
            *deg_count += 1;

            adj_list
                .entry(now_node)
                .or_insert_with(Vec::new)
                .push(next_node);
        }
    }

    let mut isolated = VecDeque::new();

    for (&index, &deg_count) in &deg {
        if deg_count == 0 {
            isolated.push_front(index);
        }
    }

    //println!("{:?}", deg);

    let node_count = n * (n - 1) / 2;
    let mut topological_order = vec![];
    while isolated.len() != 0 {
        let next = isolated.pop_back().unwrap();
        topological_order.push(next);

        let next_adj_list = adj_list.get(&next).unwrap();
        for i in next_adj_list {
            //println!("{:?} {}", next, deg.get(i).unwrap());
            let count = deg.entry(*i).or_insert(0);
            *count -= 1;
            if *count == 0 {
                isolated.push_front(*i);
            }
        }
    }

    if node_count != topological_order.len() {
        println!("-1");
        return;
    }

    let mut dists: HashMap<(usize, usize), usize> = HashMap::new();
    for &i in &topological_order {
        let adj_nodes = adj_list.get(&i).unwrap();

        let main_dist_tmp = dists.entry(i).or_insert(1);
        let main_dist = *main_dist_tmp;

        let mut visited: HashMap<(usize, usize), bool> = HashMap::new();
        for j in adj_nodes {
            //println!("{:?} {:?}", i, j);
            let dist = dists.entry(*j).or_insert(main_dist + 1);
            *dist = cmp::max(main_dist + 1, 1);

            ans = cmp::max(ans, *dist);
        }
        //println!("{:?}", dists);
    }

    println!("{}", ans);
}

fn main() {
    let thd = std::thread::Builder::new().stack_size(104_857_600);
    thd.spawn(|| solve()).unwrap().join().unwrap();

    /*
    // 入力を一括で読み込む場合
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut input = buf.split_whitespace();

    // inputに対しnext()で読み込んでいく
    let q: usize = input.next().unwrap().parse().unwrap();
    */
}

const LARGE_PRIME: u64 = 1_000_000_007;

// @〜でsnippet
fn topological_sort(n: usize, edges: &[(usize, usize)]) -> Vec<usize> {
    let mut result = vec![];
    let mut isolated = VecDeque::new();

    // to[x] = [a,b] x -> a, x -> b が存在
    let mut to = vec![vec![]; n + 1];

    // deg[x] = a -> x, b -> xのような辺の数
    let mut deg = vec![0; n + 1];
    for e in edges {
        to[e.0].push(e.1);
        deg[e.1] += 1;
    }

    for i in 1..n + 1 {
        if deg[i] == 0 {
            isolated.push_front(i);
        }
    }

    while isolated.len() != 0 {
        let next = isolated.pop_back().unwrap();
        result.push(next);
        for i in &to[next] {
            deg[*i] -= 1;
            if deg[*i] == 0 {
                isolated.push_front(*i);
            }
        }
    }

    result
}


Measured memory_bytes: 197732