/*
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*/

#include <bits/stdc++.h>
#include <functional>
#include <iomanip>
using namespace std;
	
#define int long long
#define pb push_back
#define F first
#define S second
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define REP(i,n) FOR(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define SORT(c) sort((c).begin(),(c).end())
#define ve vector
#define vi vector<int>
#define vp vector<pair<int,int>>
#define vvi vector<vector<int>>

template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>; 
using ll = long long;
ll INF = LLONG_MAX / 4000 - 100;
ll mod = 1e9 + 7;
int dx[] = {-1,0,1,0}, dy[] = {0,1,0,-1};
vector<ll> prime;
	
class fact {
public:
	int fmod = 1e9+7;
	vector<int> fac, inv;
	fact (int n, int Mod = 1e9+7) {
		fmod = Mod;
		fac = vector<int>(n,0);
		inv = vector<int>(n,0);
		fac[0] = 1; for (int i = 1; i < n; i++) fac[i] = fac[i-1] * i % fmod;
		for (int i = 0;i < n;i++) inv[i] = fact::POW(fac[i],fmod-2);
	}
	ll nCr(ll n, ll r) {if(n < r) return 0; return (fac[n] * inv[r] % fmod) * inv[n-r] % fmod;}
	ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%fmod;}a = a * a%fmod; b >>= 1;}return c;}
    inline int operator [] (int i) {return fac[i];}
};
	
template <class T = ll> T in() {T x; cin >> x; return (x);}
void DEBUG(vector<int> a) {for(int i=0;i<a.size();i++)cout<<a[i]<<" ";cout<<endl;}
void EMP(int x) {cout<<"!!!"<<x<<"!!!"<<endl;}
ll GCD(ll a, ll b) {ll c; while (b != 0) {c = a % b; a = b; b = c;}return a;}
ll LCM(ll a, ll b) {return (a / GCD(a, b)) * (b / GCD(a, b)) * GCD(a, b);}
ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%mod;}a = a * a%mod; b >>= 1;}return c;}
void PRI(ll n) {bool a[n + 1LL]; for (int i = 0; i < n + 1LL; i++) {a[i] = 1LL;}for (int i = 2; i < n + 1LL; i++) {if (a[i]) {prime.pb(i); ll b = i; while (b <= n) {a[b] = 0; b += i;}}}}
template <typename T> T chmin(T& a, T b) {if(a>b)a=b;return a;}
template <typename T> T chmax(T& a, T b) {if(a<b)a=b;return b;}
bool isSqrt(ll a) {return pow(sqrt(a),2) == a ? 1 : 0;}
void YesNo(bool a) {if (a) cout << "Yes"; else cout << "No"; cout << endl;}
void yesno(bool a) {if (a) cout << "yes"; else cout << "no"; cout << endl;}
void YESNO(bool a) {if (a) cout << "YES"; else cout << "NO"; cout << endl;}
double dis(int x1, int x2, int y1, int y2) {
	return sqrt((double)abs(x1-x2)*(double)abs(x1-x2)+(double)abs(y1-y2)*(double)abs(y1-y2));
}

class topological {
public:
    bool uniq = true, can = true;
    int n;
    set<pair<int,int>> cnt;
    vector<pair<int,int>> in;
    vector<vector<int>> loute;
    vector<int> res;
	vector<int> leng;

    topological (vector<vector<int>> lt) {
        loute = lt;
        n = loute.size();
        in = vector<pair<int,int>>(n);
		leng = vector<int>(n,1);
        for (int i = 0; i < n; i++) {
            in[i].second = i;
        }
        for (auto&& from : loute) {
            for (auto&& to : from) {
                in[to].first++;
            }
        }
        for (int i = 0; i < n; i++) {
            cnt.insert(in[i]);
        }
    }

    void run() {
        while (!cnt.empty()) {
            auto itr = cnt.begin();
            auto head = *itr;
            res.push_back(head.second);
            if (head.first != 0) can = false;
            itr = cnt.erase(itr);
            if (cnt.size() > 1) {
                if ((*itr).first == 0) uniq = false;
            }
            for (auto&& to : loute[head.second]) {
                if (in[to].first == 0) {
                    can = false;
                    break;
                }
                cnt.erase(in[to]);
                in[to].first--;
				chmax(leng[to],leng[head.second] + 1);
                cnt.insert(in[to]);
            }
        }
    }
};

bool solve() {
	int n; cin >> n;
	int ma[n][n];
	int p = 0;
	REP (i,n) {
		FOR (j,i+1,n) {
			ma[i][j] = p;
			p++;
		}
	}
	vector<vector<int>> ed(n*(n-1)/2);
	int A[n][n-1];
	REP (i,n) {
		REP (j,n - 1) {
			int a; cin >> a;
			A[i][j] = --a;
		}
	}
	REP (i,n) {
		FOR (j,1,n-1) {
			int mae = A[i][j-1];
			int ato = A[i][j];
			// cout << ma[{min(i,mae),max(i,mae)}] << " " << ma[{min(i,ato),max(i,ato)}] << endl;
			ed[ma[min(i,mae)][max(i,mae)]].pb(ma[min(i,ato)][max(i,ato)]);
		}
	}
	topological topo(ed);
	topo.run();
	if (topo.can) {
		int ans = 0;
		REP (i,(n*(n-1)/2)) {
			chmax(ans,topo.leng[i]);
		}
		cout << ans << endl;
	} else {
		cout << -1 << endl;
	}
}

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	solve();
}


Measured memory_bytes: 140416