#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#define int long long
#define mkp make_pair
#define pb push_back
#define ff first
#define ss second
#define debug1(a) cout<<a<<endl;
#define debug2(a,b) cout<<a<<' '<<b<<endl;
#define debug3(a,b,c) cout<<a<' '<<b<<' '<<c<<endl;
#define rep(i,n) for(int i=0;i<n;i++)
#define repr(i,a,b)for(int i=a;i<b;i++)
#define repre(i,a,b)for(int i=a;i<=b;i++)
#define pi pair<int,int>
#define pii pair<int,pi>
#define all(v) v.begin(),v.end()
#define pq priority_queue
#define mpq priority_queue<int,vector<int>,greater<int> >
#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
using namespace __gnu_pbds;
using namespace std;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> orderedSet;
typedef tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update> orderedMSet;
//*p.find_by_order(index) return value at index
//p.order_of_key(key) return index
const int maxn=1009;
int dp[maxn];
int arr[maxn][maxn];
int visited[maxn];
int n;
int check(int day)
{
  //cout<<day<<endl;
  repre(i,0,n)dp[i]=1;
  int match=0;
  int c=0;
  while(day--)
  {
    repre(i,0,n)visited[i]=0;
    match=0;
    repre(i,1,n)
    {
      if(dp[i]==n || visited[i]==1)continue;
      int oppo=arr[i][dp[i]];
      if(visited[oppo] || dp[oppo]==n)continue;
      int uskaoppo=arr[oppo][dp[oppo]];
      if(uskaoppo==i)
      {
        visited[i]=1;
        visited[oppo]=1;
        dp[i]++;
        dp[oppo]++;
        if(dp[i]==n)c++;
        if(dp[oppo]==n)c++;
        match=1;
      }
    }
    if(c==n)break;
    if(match==0)return -1;
  }
  if(c==n)return 1;
  return 0;
}
int32_t main()
{
  //freopen("input.txt", "r", stdin);
  //freopen("output.txt", "w", stdout);
  fastio
  cin>>n;
  repre(i,1,n)
  {
    repre(j,1,n-1)
    {
      cin>>arr[i][j];
    }
  }
  int low=1;
  int high=(n*(n-1))/2;
  int temp;
  int flag=0;
  while(low<high)
  {
    int mid=(low+high)/2;
    temp=check(mid);
    if(temp==-1)
    {
      flag=1;
      break;
    }
    if(temp==1)high=mid;
    else low=mid+1;
  }
  if(flag==1)cout<<"-1"<<'\n';
  else
  cout<<low<<'\n';
  return 0;
}