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

#define REP(i,m,n) for(int i=(m); i<(int)(n); i++)
#define RREP(i,m,n) for(int i=(int)(n-1); i>=m; i--)
#define rep(i,n) REP(i,0,n)
#define rrep(i,n) RREP(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define aut(r,v) __typeof(v) r = (v)
#define each(it,o) for(aut(it,(o).begin()); it!=(o).end(); ++it)
#define reach(it,o) for(aut(it,(o).rbegin()); it!=(o).rend(); ++it)
#define fi first
#define se second
#define debug(...) {cerr<<"[L"<<__LINE__<<"] "; _debug(__VA_ARGS__);}

template<typename T1, typename T2> ostream& operator<<(ostream& o, const pair<T1, T2>& p)
{return o<<"("<<p.first<<", "<<p.second<<")";}
template<typename T>string join(const vector<T>&v, string del=", ")
{stringstream s;rep(i,v.size())s<<del<<v[i];return s.str().substr(del.size());}
template<typename T>ostream& operator<<(ostream& o, const vector<T>&v)
{if(v.size())o<<"["<<join(v)<<"]";return o;}
template<typename T>ostream& operator<<(ostream& o, const vector<vector<T> >&vv)
{int l=vv.size();if(l){o<<endl;rep(i,l){o<<(i==0?"[ ":",\n  ")<<vv[i]<<(i==l-1?" ]":"");}}return o;}
template<typename T>ostream& operator<<(ostream& o, const set<T>& st)
{vector<T> v(st.begin(),st.end());o<<"{ "<<join(v)<<" }";return o;}
template<typename T1, typename T2>ostream& operator<<(ostream& o, const map<T1, T2>& m)
{each(p,m){o<<(p==m.begin()?"{ ":",\n  ")<<*p<<(p==--m.end()?" }":"");}return o;}
inline void _debug(){cerr<<endl;}
template<class First, class... Rest>
void _debug(const First& first, const Rest&... rest){cerr<<first<<" ";_debug(rest...);}

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;

const double PI = (1*acos(0.0));
const double EPS = 1e-9;
const ll INF = 0x3f3f3f3f;
const ll INFL = 0x3f3f3f3f3f3f3f3fLL;
const ll mod = 1e9 + 7;

inline void finput(string filename) {
    freopen(filename.c_str(), "r", stdin);
}

const int MAX_V = 1000000;

int n;
vvi g;
vi tsort(){
    vi indeg(n*n, 0);
    stack<int> S;
    REP(i,0,n-1) REP(j,i+1,n) for(auto v : g[n*i+j]) indeg[v]++;
    REP(i,0,n-1) REP(j,i+1,n) if(indeg[n*i+j] == 0) S.push(n*i+j);

    vi res;
    while(S.size()>0){
        int v = S.top(); S.pop();
        res.emplace_back(v);
        for(auto u : g[v]){
            indeg[u]--;
            if(indeg[u] == 0) S.push(u);
        }
    }
    return res;
}

vi d;
void dfs(int v){
    if(d[v] != 0) return;
    int res = 1;
    for(auto u : g[v]){
        if(d[u] == 0) dfs(u);
        res = max(res, d[u]+1);
    }
    d[v] = res;
}

int main(){
    ios_base::sync_with_stdio(0);
    // finput("./input");
    cin >> n;
    g = vvi(n*n);
    rep(i,n){
        vi a(n-1);
        rep(j,n-1) cin >> a[j];
        rep(j,n-2){
            int froml = i;
            int fromr = a[j]-1;
            if(froml > fromr) swap(froml, fromr);
            int tol = i;
            int tor = a[j+1]-1;
            if(tol > tor) swap(tol, tor);
            g[n*froml+fromr].push_back(n*tol+tor);
        }
    }
    vi topo = tsort();
    if(topo.size() != n*(n-1)/2){
        cout << -1 << endl;
        return 0;
    }

    d = vi(n*n, 0);
    REP(i,0,n-1) REP(j,i+1,n){
        dfs(n*i+j);
    }
    int ans = 0;
    REP(i,0,n-1) REP(j,i+1,n) ans = max(ans, d[n*i+j]);
    cout << ans << endl;
    return 0;
}

Measured memory_bytes: 45436