#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Edge = pair<int, int>;
using Graph = vector<vector<Edge>>;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define RSORT(v) sort((v).rbegin(), (v).rend())
const ll MOD = 1000000007;
const ll nmax = 8;
const ll INF = 1e9;
bool graph[nmax][nmax];
vector<vector<ll>> dist = vector<vector<ll>>(nmax, vector<ll>(nmax, INF));
void warshall_floyd(ll n)
{
    for (size_t i = 0; i < n; i++)
    {
        for (size_t j = 0; j < n; j++)
        {
            for (size_t k = 0; k < n; k++)
            {
                dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);
            }
        }
    }
}

class UnionFind
{
public:
    vector<ll> Parent;

    UnionFind(ll N)
    {
        Parent = vector<ll>(N, -1);
    }
    ll find(ll A)
    {
        if (Parent[A] < 0)
            return A;
        return Parent[A] = find(Parent[A]);
    }

    ll size(ll A)
    {
        return -Parent[find(A)];
    }

    bool Union(ll A, ll B)
    {
        A = find(A);
        B = find(B);
        if (A == B)
        {
            return false;
        }
        if (size(A) < size(B))
            swap(A, B);

        Parent[A] += Parent[B];
        Parent[B] = A;

        return true;
    }
};

ll gcd(ll a, ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

ll lcm(ll a, ll b)
{
    ll g = gcd(a, b);
    return a / g * b;
}

ll mulMod(ll a, ll b)
{
    return (((a % MOD) * (b % MOD)) % MOD);
}

ll powMod(ll a, ll p)
{
    if (p == 0)
    {
        return 1;
    }
    else if (p % 2 == 0)
    {
        ll half = powMod(a, p / 2);
        return mulMod(half, half);
    }
    else
    {
        return mulMod(powMod(a, p - 1), a);
    }
}

ll ceil(ll a, ll b)
{
    return (a + b - 1) / b;
}
const int MAXN = 1005;
const int MAXV = MAXN * (MAXN - 1) / 2;
vector<int> to[MAXV];
int id[MAXN][MAXN];
int toId(int i, int j)
{
    if (i > j)
        swap(i, j);
    return id[i][j];
}
bool visited[MAXV];
bool calculated[MAXV];
int dp[MAXV];
int dfs(int v)
{
    if (visited[v])
    {
        if (!calculated[v])
        {
            return -1;
        }
        else
        {
            return dp[v];
        }
    }
    visited[v] = true;
    dp[v] = 1;

    for (int u : to[v])
    {
        int res = dfs(u);
        if(res == -1) return -1;
        dp[v] = max(dp[v], dfs(u) + 1);
    }
    calculated[v] = true;
    return dp[v];
}
int main()
{
    long long N;
    scanf("%lld", &N);
    vector<vector<int>> a(N, vector<int>(N - 1));
    rep(i, N)
    {
        rep(j, N - 1)
        {
            cin >> a[i][j];
            a[i][j]--;
        }
    }
    Graph G;
    int V = 0;
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N; j++)
        {
            if (i < j)
            {
                id[i][j] = V++;
            }
        }
    }
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N - 1; j++)
        {
            a[i][j] = toId(i, a[i][j]);
        }
        for (int j = 0; j < N - 2; j++)
        {
            to[a[i][j]].push_back(a[i][j + 1]);
        }
    }
    int ans = 0;
    for (int i = 0; i < V; i++)
    {
        int res = dfs(i);
        if(res == -1){
            cout << -1 << endl;
            return 0;
        }
        ans = max(dfs(i), ans);
    }
    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 38528