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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program main
    implicit none
    integer:: N,i, no, day
    logical:: battle, flag
    integer, allocatable:: A(:,:), noind(:)
    logical, allocatable:: isbattled(:)
    no = 0
    read*, N
    allocate(A(N,N-1), noind(N), isbattled(N))

    do i=1,N
        read*, A(i,1:N-1)
    enddo
    noind(1:N) = 1 
    day = 1
    battle = .true.
    do while(.true.)
        ! print*, '--- ---day', day, battle
        battle = .false.
        isbattled(1:N) = .false.
        do i = 1, N
            if((noind(i)) == N) cycle
            if(isbattled(i) .eqv. .true.) cycle
            no = A(i, noind(i))
            if(isbattled(no) .eqv. .true.) cycle

            if(A(no, noind(no)) == i)then
                ! print*, i , 'vs' ,no
                noind(i) = noind(i) + 1
                noind(no) = noind(no) + 1
                isbattled(i) = .true.
                isbattled(no) = .true.
                battle = .true.
            endif
        enddo

        if (.not. battle) then
            day = day - 1
            exit
        end if

        day = day + 1
    enddo

    ! print*, noind
    flag = .true.
    do i = 1, N
        if(noind(i) /= N)then
            flag = .false.
        endif
    enddo

    if(flag) then
        print'(i0)',day
    else
        print*, '-1'
    endif


end program