#include <algorithm>
#include <functional>
#include <iostream>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <unordered_set>
#include <queue>
#include <numeric>
#include <bitset>
#include <cmath>

using namespace std;
using ll = long long;
using ull = unsigned long long;
// const ll mod =  998244353 ;
const ll mod =  1000000007 ;
const ll inf = 1e18;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, 1, -1};


#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REP_FROM(i, j, n) for (ll i = (j); i < (n); ++i)
#define REP_REV(i, n) for (ll i = n-1; i >= 0; --i)
#define REP_FROM_REV(i, j, n) for (ll i = n-1; i >= j; --i)
#define all(x) (x).begin(),(x).end()
#define sz(x) ll(x.size())
template<typename T> inline T chmax(T& a, const T b) { return a = (a < b) ? b : a; }
template<typename T> inline T chmin(T& a, const T b) { return a = (a > b) ? b : a; }

ll power(ll base, ll exponent){ if(exponent % 2){ return power(base, exponent - 1) * base % mod; }else if(exponent){ ll root_ans = power(base, exponent / 2); return root_ans * root_ans % mod; }else{ return 1; }}
ll inverse(ll x){ return power(x, mod - 2);}
ll gcd(ll a, ll b) {if(a < b) gcd(b, a);ll r;while(r=a%b) {a=b;b=r;}return b;}
template<typename T> ll sum(T begin, T end) {return accumulate(begin, end, 0ll);}
struct combination{ vector<ll> fact, inv; combination(int sz) : fact(sz + 1), inv(sz + 1){ fact[0] = 1; for(int i = 1; i <= sz; i++){ fact[i] = fact[i - 1] * i % mod; } inv[sz] = power(fact[sz], mod - 2); for(int i = sz - 1; i >= 0; i--){ inv[i] = inv[i + 1] * (i + 1) % mod; } } ll C(int p, int q) const{ if(q < 0 || p < q) return 0; return (fact[p] * inv[q] % mod * inv[p - q] % mod); } };

using Pair = pair<ll, ll>;

template <ll Modulus> struct ModInt {
    ll a;
    constexpr ModInt(const ll x = 0) noexcept  : a((x%mod+mod) % mod){}
    constexpr ll &value() noexcept {return a;}
    constexpr const ll &value() const noexcept {return a;}
    constexpr ModInt operator+(const ModInt x) const noexcept {
      return ModInt(*this) += x;
    }
    constexpr ModInt operator-(const ModInt x) const noexcept {
      return ModInt(*this) -= x;
    }
    constexpr ModInt operator*(const ModInt x) const noexcept {
      return ModInt(*this) *= x;
    }
    constexpr ModInt operator/(const ModInt x) const noexcept {
      return ModInt(*this) /= x;
    }
    constexpr ModInt &operator+=(const ModInt x) noexcept {
      a += x.a;
      if (a >= Modulus) {
        a -= Modulus;
      }
      return *this;
    }
    constexpr ModInt &operator-=(const ModInt x) noexcept {
      if (a < x.a) {
        a += Modulus;
      }
      a -= x.a;
      return *this;
    }
    constexpr ModInt &operator*=(const ModInt x) noexcept {
      a = a * x.a % Modulus;
      return *this;
    }
    constexpr ModInt &operator/=(ModInt x) noexcept {
      ll exp = Modulus - 2;
      while (exp) {
        if (exp % 2) {
          *this *= x;
        }
        x *= x;
        exp /= 2;
      }
      return *this;
    }
    constexpr  ModInt operator-() noexcept {
      return ModInt(-a);
    }
    friend ostream& operator<<(ostream& os, const ModInt& m){
      os << m.a;
      return os;
    }
};
using mint = ModInt<mod>;

struct DAG {
    int n;
    vector<vector<int>> adj;
    vector<int> sorted;
    bool isAcyclic = true;
    vector<int> visited;
    DAG(vector<vector<int>>& adj) : n(adj.size()),adj(adj),visited(adj.size()) {}
    void dfs(int v) {
      if (visited[v] == 2) {
        isAcyclic = false;
        return;
      } else if (!visited[v]) {
        visited[v] = 2;
        for (int s : adj[v]) {
          dfs(s);
        }
        visited[v] = 1;
        sorted.push_back(v);
      }
    }
    void tsort() {
      for (int i = 0; i < n; i++) {
        if (!visited[i]) dfs(i);
      }
      reverse(all(sorted));
    }
};

vector<vector<int>> g;
vector<int> dp;
vector<int> visited;
vector<int> calculated;
int dfs(int cur) {
  if(calculated[cur]) return dp[cur];
  if(visited[cur] && calculated[cur] == 0) return -1;
  visited[cur] = 1;
  dp[cur] = 1;
  for(int p: g[cur]) {
    int v = dfs(p);
    if(v == -1) return -1;
    dp[cur] = max(dp[cur], v+1);
  }
  calculated[cur] = 1;
  return dp[cur];
}

signed main() {
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  ll n;
  cin >> n;
  g.resize(n*(n-1));
  dp.resize(n*(n-1));
  visited.resize(n*(n-1));
  calculated.resize(n*(n-1));
  auto toId = [&](int a, int b) {
      if (a > b) swap(a, b);
      return a * n + b;
  };
  REP(i, n) {
    int a;
    cin >> a;
    a--;
    int prev = toId(i, a);
    REP(j, n-2) {
      int b;
      cin >> b;
      b--;
      int cur = toId(i, b);
      g[prev].push_back(cur);
      prev = cur;
    }
  }
  DAG dag(g);
  dag.tsort();
  if(!dag.isAcyclic) {
    cout << -1 << endl;
    return 0;
  }
  auto ans = 0;
  REP(i, n*(n-1)) {
    int v = dfs(i);
//    if(v < 0) {
//      ans = -1;
//      break;
//    }
    ans = max(ans, v);
  }
  cout << ans << endl;
  return 0;
}


Measured memory_bytes: 100084