Problem:
Score : 500 points

Problem Statement

N players will participate in a tennis tournament. We will call them Player 1, Player 2, \ldots, Player N.

The tournament is round-robin format, and there will be N(N-1)/2 matches in total.
Is it possible to schedule these matches so that all of the following conditions are satisfied? If the answer is yes, also find the minimum number of days required.

Each player plays at most one matches in a day.

Each player i (1 \leq i \leq N) plays one match against Player A_{i, 1}, A_{i, 2}, \ldots, A_{i, N-1} in this order.

Constraints

3 \leq N \leq 1000

1 \leq A_{i, j} \leq N

A_{i, j} \neq i

A_{i, 1}, A_{i, 2}, \ldots, A_{i, N-1} are all different.

Input

Input is given from Standard Input in the following format:

N
A_{1, 1} A_{1, 2} \ldots A_{1, N-1}
A_{2, 1} A_{2, 2} \ldots A_{2, N-1}
:
A_{N, 1} A_{N, 2} \ldots A_{N, N-1}

Output

If it is possible to schedule all the matches so that all of the conditions are satisfied, print the minimum number of days required; if it is impossible, print -1.

Sample Input 1

3
2 3
1 3
1 2

Sample Output 1

3

All the conditions can be satisfied if the matches are scheduled for three days as follows:

Day 1: Player 1 vs Player 2

Day 2: Player 1 vs Player 3

Day 3: Player 2 vs Player 3

This is the minimum number of days required.

Sample Input 2

4
2 3 4
1 3 4
4 1 2
3 1 2

Sample Output 2

4

All the conditions can be satisfied if the matches are scheduled for four days as follows:

Day 1: Player 1 vs Player 2, Player 3 vs Player 4

Day 2: Player 1 vs Player 3

Day 3: Player 1 vs Player 4, Player 2 vs Player 3

Day 4: Player 2 vs Player 4

This is the minimum number of days required.

Sample Input 3

3
2 3
3 1
1 2

Sample Output 3

-1

Any scheduling of the matches violates some condition.

Solution in PyPy3 (2.4.0) (judge verdict: Time Limit Exceeded)

import queue
import copy

N=int(input())
A=[[] for _ in range(N)]

for i in range(N):
    A[i]=list(map(int,input().split()))

NE=[0]*N#i番目の人が，次何番目の試合をするかのリスト
F=[0]*N#i番目の人が，該当する日に試合をしたか記憶しておく

#i+1日目の試合をする人はi日目に試合をした人なので，それを記憶．
q1=queue.Queue()
q2=queue.Queue()

#初日
for i in range(N):
    opp=A[i][0]-1
    if A[opp][0]-1==i:
        NE[i]+=1
        q1.put(i)

ans=1
#d日目
for d in range(N*(N-1)//2):
    F=[0]*N
    while not q2.empty():
        a=q2.get()
        q1.put(a)
    while not q1.empty():
        i=q1.get()
        if NE[i]==N-1:
            continue
        opp=A[i][NE[i]]-1
        if F[i]==1 or F[opp]==1:#その日に試合したことがある人はスルー,oppの重複防止
            continue
        if A[opp][NE[opp]]-1==i:
            NE[i]+=1
            NE[opp]+=1
            F[i]=1
            F[opp]=1
            if NE[i]!=N-1:
                q2.put(i)
            if NE[opp]!=N-1:
                q2.put(opp)
    ans+=1
    if q2.empty() and q2.empty():
        break

for i in range(N):
    if NE[i]!=N-1:
        ans=-1
print(ans)