#include <bits/stdc++.h>
using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef long long LL;
typedef pair<int, int> PII;
typedef pair<LL,LL> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef vector<bool> VB;
typedef vector<VB> VVB;
typedef vector<double> VD;
typedef vector<VD> VVD;
typedef vector<string> VS;
typedef vector<VS> VVS;
typedef vector<char> VC;
typedef vector<VC> VVC;
typedef vector<PII> VPII;
typedef vector<PLL> VPLL;
typedef priority_queue<int> PQGI; //大きい順
typedef priority_queue<int, VI, greater<int>> PQLI;
typedef priority_queue<PII> PQGP;
typedef priority_queue<PII, VPII, greater<int>> PQLP;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EB emplace_back
#define PB push_back
#define PF push_front
#define POB pop_back
#define POF pop_front
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define SORTR(c) sort((c).rbegin(), (c).rend())
#define LB lower_bound
#define UB upper_bound
#define NEXP next_permutation
#define FI first
#define SE second
#define Vmin(a) *min_element((a).begin(),(a).end())
#define Vmax(a) *max_element((a).begin(),(a).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define FORR(i,a,b) for(int i = (b-1);i>=(a);i--)
#define REPR(i,n) FORR(i,0,n)
#define CFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define CREP(i,n)  CFOR(i,0,n)
#define CFORR(i,a,b) for(int i = (b);i>=(a);i--)
#define CREPR(i,n) CFORR(i,0,n)
#define BFOR(bit,a,b) for(int bit = (a); bit < (1<<(b)); ++bit)
#define BREP(bit,n) BFOR(bit,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);
const int INF = INT_MAX/2;
const LL LINF = LLONG_MAX/3;
const int RINF = INT_MIN/2;
const LL RLINF = LLONG_MIN/3;
const LL MOD = 1e9+7;
const LL MODD = 998244353;
const int MAX = 510000;

inline bool Eq(double a, double b) { return fabs(b - a) < EPS; }

//other
//-------------------------------------------
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define COUT(x) cout << (x) << endl
#define COUT2(x,y) cout << (x) << " " << (y) << endl
#define COUT3(x,y,z) cout << (x) << " " << (y) << " " << (z) << endl
#define PR(x) cout << (x)
#define ENDL cout << endl
#define SPACE cout << " "
#define BC(x) __builtin_popcountll(x)


VI dx = {1,0,-1,0,1,1,-1,-1};
VI dy = {0,1,0,-1,1,-1,1,-1};
VC dc = {'R','D','L','U'};
VS ds = {"R","D","L","U","RD","RU","LD","LU"};

LL Gcd(LL a, LL b) {return __gcd(a,b);}
LL Lcm(LL a, LL b) {return a/Gcd(a,b)*b;}

LL ModPow(LL A, LL N, LL M){
  LL res = 1;
  while(N>0){
    if(N&1) res = res * A % M;
    A = A * A % M;
    N >>= 1;
  }
  return res;
}


template<class T> void VCout(vector<T> &v){
  int N = SZ(v);
  REP(i,N){
    cout << v.at(i);
    if(i == N-1) cout << endl;
    else cout << " ";
  }
  return;
}

int f(int a, int b, int n){
  return (2*(n-1)-a+1)*a/2+b-a-1;
}

VI TopoSort(VVI &G){
  VI ans;
  int n = SZ(G);
  VI ind(n,0);
  REP(i,n){
    for(auto e : G.at(i)){
      ind.at(e)++;
    }
  }
  queue<int> que;
  REP(i,n){
    if(ind.at(i)==0) que.push(i);
  }
  while(!que.empty()){
    int now = que.front(); que.pop();
    ans.PB(now);
    for(auto e : G.at(now)){
      ind.at(e)--;
      if(ind.at(e)==0) que.push(e);
    }
  }
  return ans;
}

int dfs(VVI &G, int i, VI &dp){
  if(dp.at(i) >= 0) return dp.at(i);
  int res = 0;
  for(auto e : G.at(i)){
    chmax(res,dfs(G,e,dp)+1);
  }
  return dp.at(i) = res;
}


int main() {

  // cin.tie(0);
  // ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  int N; cin >> N;

  VVI G(N*(N-1)/2);
  VVI A(N,VI(N-1));
  REP(i,N)REP(j,N-1){
    int a; cin >> a;
    A.at(i).at(j) = --a;
  }

  REP(i,N)REP(j,N-2){
    int a = i, b = i;
    int now = A.at(i).at(j);
    int nec = A.at(i).at(j+1);
    if(a > now) swap(a,now);
    if(b > nec) swap(b,nec);
    G.at(f(a,now,N)).PB(f(b,nec,N));
//    COUT2(f(a,now,N),f(b,nec,N));
  };

  int ans = 0;
  VI res = TopoSort(G);
  if(SZ(res)!=N*(N-1)/2){
    ans = -1;
  }

  VI dp(N*(N-1)/2,-1);

  if(ans == 0){
    REP(i,N*(N-1)/2){
      chmax(ans,dfs(G,i,dp)+1);
    }
  }

  COUT(ans);

  return 0;
}


Measured memory_bytes: 35576