#include<bits/stdc++.h>
using namespace std;using ll=long long;using vi=vector<int>;using vvi=vector<vi>;using vl=vector<ll>;using vvl=vector<vl>;using P=pair<int,int>;using PL=pair<ll,ll>;using vp=vector<P>;using vpl=vector<PL>;
template<typename T>constexpr auto inf=numeric_limits<T>::max()/2;constexpr int INF=inf<int>,MOD=1000000007;constexpr ll LINF=inf<ll>;
#define _ol3(_1,_2,_3,name,...)name
#define _rep(i,n)_repi(i,0,n)
#define _repi(i,a,b)for(int i=a,i##_l=(b);i<i##_l;++i)
#define REP(...)_ol3(__VA_ARGS__,_repi,_rep,)(__VA_ARGS__)
#define REPR(i,n)for(int i=n-1;i>=0;--i)
#define REPA(i,v)REP(i,v.size())
#define all(v)(v).begin(),(v).end()
#define bit(n)(1ll<<(n))
#define uniq(v)sort(all(v));v.erase(unique(all(v)),v.end())
#define F first
#define S second
#define endl '\n'
#define cho(n,a,b)cout<<((n)?a:b)<<endl
void YES(int n){cho(n,"YES","NO");}void Yes(int n){cho(n,"Yes","No");}void Poss(int n){cho(n,"Possible","Impossible");}
void _print(ostream&){}template<class T,class...U>void _print(ostream&s,T&&t,U&&...u){s<<t<<(sizeof...(u)?' ':'\n');_print(s,u...);}
template<class...T>void print(T&&...t){_print(cout,t...);}
#ifndef LOCAL
struct osd{template<class T>osd&operator<<(const T&t){return*this;}};osd cer_;
#define dprint(...)
#define cerr cer_
#else
template<class...T>void dprint(T&&...t){_print(cerr,t...);}
#endif
template<class T>bool chmax(T&a,const T&b){if(a<b){a=b;return 1;}return 0;}template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>ostream&operator<<(ostream&o,const vector<T>&v){for(auto&&i:v)o<<i<<' ';return o;}
template<class T>istream&operator>>(istream&i,vector<T>&v){for(T&j:v)i>>j;return i;}
template<class T,class U>ostream&operator<<(ostream&o,const pair<T,U>&p){return o<<p.F<<' '<<p.S;}
template<class T,class U>istream&operator>>(istream&i,pair<T,U>&p){return i>>p.F>>p.S;}
template<class T>ostream&operator<<(ostream&o,const set<T>&v){for(auto&&i:v)o<<i<<' ';return o;}
template<class T>ostream&operator<<(ostream&o,const multiset<T>&v){for(auto&&i:v)o<<i<<' ';return o;}
template<class T>vector<T>&operator<<(vector<T>&v,const T&t){v.push_back(t);return v;}
template<class T>set<T>&operator<<(set<T>&v,const T&t){v.insert(t);return v;}
template<class T>multiset<T>&operator<<(multiset<T>&v,const T&t){v.insert(t);return v;}

int get_v(int i, int j){if(i>j)swap(i,j);return i*1000+j;}

int main(){
    cin.tie(0);ios::sync_with_stdio(0);cout<<fixed<<setprecision(10);
    int n;
    cin>>n;

    int v=n*1000;
    vi h(v);
    vi ans(v, -1);
    vvi g(v);

    vvi a(n, vi(n-1));
    REP(i,n)REP(j,n-1){cin>>a[i][j];--a[i][j];}

    REP(i,n){
        REP(j,n-2){
            g[get_v(i,a[i][j])].push_back(get_v(i,a[i][j+1]));
            ++h[get_v(i,a[i][j+1])];
        }
    }

    stack<int> st;
    REP(i,n)REP(j,i+1,n)if(h[get_v(i,j)]==0){
        st.push(get_v(i,j));
        ans[get_v(i,j)]=1;
        dprint(i,',',j);
    }
    int c=0;
    while(!st.empty()){
        if(++c>3000*n){
            print(-1);
            return 0;
        }
        int i=st.top();
        st.pop();
        for(int x:g[i]){
            //隣接する頂点の入次数をマイナス1
            h[x]--;
            //これによって入次数が0になればstに追加
            chmax(ans[x], ans[i]+1);
            if(h[x] == 0){
                st.push(x);
            }
        }
    }

    // end
    int ma=0;
    REP(i,n)REP(j,i+1,n){
        if(ans[get_v(i,j)]<0){
            print(-1);
            return 0;
        }
        chmax(ma, ans[get_v(i,j)]);
        dprint(i,',',j, ans[get_v(i,j)]);
    }
    print(ma);
    return 0;
}


Measured memory_bytes: 51072