#![allow(non_snake_case, unused)]
use std::cmp::*;
use std::collections::*;
use std::f64::consts::*;

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)*}
    };

    ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($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, [ $t:tt ]) => {
        {
            let len = read_value!($next, usize);
            (0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
        }
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

//topological sort
fn dfs(
    graph: &Vec<Vec<usize>>,
    cur: usize,
    visited: &mut Vec<usize>,
    sorted: &mut Vec<usize>,
    is_acyclic: &mut bool,
) {
    if visited[cur] == 1 {
        *is_acyclic = true;
    } else if visited[cur] == 0 {
        visited[cur] = 1;
        for &node in &graph[cur] {
            dfs(graph, node, visited, sorted, is_acyclic);
        }
        visited[cur] = 2;
        sorted.push(cur);
    }
}

fn main() {
    input! {
        n: usize,
        mut a: [[usize1; n-1]; n],
    }

    let mut g = vec![vec![]; n * (n - 1) / 2];

    let mut dict = HashMap::new();
    let mut cnt = 0;

    for i in 0..n {
        for j in i + 1..n {
            dict.insert((i, j), cnt);
            dict.insert((j, i), cnt);
            cnt += 1;
        }
    }
    for i in 0..n {
        for j in 0..n - 2 {
            g[dict[&(i, a[i][j])]].push(dict[&(i, a[i][j + 1])]);
        }
    }
    let mut visited = vec![0; n * (n - 1) / 2];
    let mut sorted = vec![];
    let mut is_acyclic = false;
    for i in 0..n * (n - 1) / 2 {
        let mut depth = 0;
        if visited[i] == 0 {
            dfs(&g, i, &mut visited, &mut sorted, &mut is_acyclic);
        }
    }
    sorted.reverse();

    let mut dp = vec![1; n * (n - 1) / 2];
    for i in 0..n * (n - 1) / 2 {
        for &node in &g[sorted[i]] {
            dp[node] = max(dp[node], dp[sorted[i]] + 1);
        }
    }

    if is_acyclic {
        println!("-1");
    } else {
        println!("{}", dp.iter().max().unwrap());
    }
}


Measured memory_bytes: 123176