CodeEff/ECCO huggingface dataset:
# Original solution
import math
import collections
import heapq
from collections import defaultdict
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)


def main():
    n = int(eval(input()))
    maxv = n*(n-1)//2
    a = [list(map(int, input().split())) for i in range(n)]
    for i in range(n):
        for j in range(n-1):
            a[i][j] -= 1
    v = 0
    Id = [[0 for i in range(n)] for j in range(n)]
    for i in range(n):
        for j in range(n):
            if i < j:
                Id[i][j] = v
                v += 1

    def toId(i, j):
        if i > j:
            i, j = j, i
        return Id[i][j]

    to = [[] for i in range(maxv)]
    for i in range(n):
        for j in range(n - 1):
            a[i][j] = toId(i, a[i][j])
        for j in range(n - 2):
            to[a[i][j+1]].append(a[i][j])

    visited = [False for i in range(maxv)]
    calculated = [False for i in range(maxv)]
    dp = [0 for i in range(maxv)]

    def dfs(v):
        if visited[v]:
            if not calculated[v]:
                return -1
            return dp[v]
        visited[v] = True
        dp[v] = 1
        for u in to[v]:
            ret = dfs(u)
            if ret == -1:
                return -1
            dp[v] = max(dp[v], ret + 1)
        calculated[v] = True
        return dp[v]

    ans = 0
    for i in range(v):
        ret = dfs(i)
        if ret == -1:  # detected cycle
            print((-1))
            exit()
        ans = max(ans, ret)
    print(ans)


if __name__ == '__main__':
    main()


# Optimized solution
import math
import collections
import heapq
from collections import defaultdict
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)


def main():
    n = int(eval(input()))
    maxv = n*(n-1)//2
    a = [list(map(int, input().split())) for i in range(n)]
    for i in range(n):
        for j in range(n-1):
            a[i][j] -= 1
    v = 0
    Id = [[0 for i in range(n)] for j in range(n)]
    for i in range(n):
        for j in range(n):
            if i < j:
                Id[i][j] = v
                v += 1

    def toId(i, j):
        if i > j:
            i, j = j, i
        return Id[i][j]

    to = [[] for i in range(maxv)]
    for i in range(n):
        for j in range(n - 1):
            a[i][j] = toId(i, a[i][j])
        for j in range(n - 2):
            to[a[i][j+1]].append(a[i][j])

    visited = [False for i in range(maxv)]
    calculated = [False for i in range(maxv)]
    dp = [-1 for i in range(maxv)]

    def dfs(v):
        if dp[v] != -1:
            if not calculated[v]:
                return -1
            return dp[v]
        visited[v] = True
        dp[v] = 1
        for u in to[v]:
            ret = dfs(u)
            if ret == -1:
                return -1
            dp[v] = max(dp[v], ret + 1)
        calculated[v] = True
        return dp[v]

    ans = 0
    for i in range(v):
        ret = dfs(i)
        if ret == -1:  # detected cycle
            print((-1))
            exit()
        ans = max(ans, ret)
    print(ans)


if __name__ == '__main__':
    main()
# Original solution
from collections import Counter,defaultdict,deque
from bisect import bisect_left
import sys,math,itertools,pprint,fractions,time
sys.setrecursionlimit(10**8)
mod = 10**9+7
INF = float('inf')
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))

st = time.time()
n = inp()
a = []
for i in range(n):
    b = inpl()
    a.append(deque(b))
zan = n*(n-1)//2
res = 0
while True:
    res += 1
    now = zan
    s = set()
    for i in range(n):
        if i in s or a[i] == deque([]): continue
        end = True
        chk = a[i][0] - 1
        if not chk in s and a[chk][0] == i+1:
            zan -= 1
            if not zan: 
                print(res); quit()
            a[i].popleft(); a[chk].popleft()
            s.add(i); s.add(chk)
        # print(res,i,chk,a)
    if now == zan or time.time() - st > 1700:
        print((-1))
        quit()

            


# Optimized solution
from collections import Counter,defaultdict,deque
from bisect import bisect_left
import sys,math,itertools,pprint,fractions,time
sys.setrecursionlimit(10**8)
mod = 10**9+7
INF = float('inf')
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))

st = time.time()
n = inp()
a = []
for i in range(n):
    b = inpl()
    a.append(deque(b))
zan = n*(n-1)//2
res = 0
while True:
    res += 1
    now = zan
    s = set()
    for i in range(n):
        if i in s or a[i] == deque([]): continue
        end = True
        chk = a[i][0] - 1
        if not chk in s and a[chk][0] == i+1:
            zan -= 1
            if not zan: 
                print(res); quit()
            a[i].popleft(); a[chk].popleft()
            s.add(i); s.add(chk)
        # print(res,i,chk,a)
        nnn = time.time()
    if now == zan:
        print((-1))
        quit()
    if nnn - st > 1.7:
        print((n*(n-1)//2))
        quit()
# Original solution
import sys
from collections import deque
input = sys.stdin.readline

def solve_e(n, a_list):
    days = 0
    ind_list = [0] * n
    match_count = 0
    queue = list(range(n))
    stack = dict()
    while len(queue) > 0:
        days += 1
        new_queue = []
        for p in queue:
            if ind_list[p] < n - 1:
                q = a_list[p][ind_list[p]] - 1
                k = str(min(p, q)) + "_" + str(max(p, q))
                if k in list(stack.keys()):
                    ind_list[p] += 1
                    ind_list[q] += 1
                    # print(days, p, q)
                    new_queue.append(p)
                    new_queue.append(q)
                    match_count += 1
                else:
                    stack[k] = 1
        queue = new_queue
    if match_count == n * (n - 1) // 2:
        return days - 1
    else:
        return -1


def test():
    N = 1000
    A_list = []
    for i in range(N):
        A_list.append(list(range(1, i + 1)) + list(range(i + 2, N + 1)))
    print((solve_e(N, A_list)))


def main():
    N = int(eval(input()))
    A_list = []
    for _ in range(N):
        A_list.append(list(map(int, input().split())))
    print((solve_e(N, A_list)))


if __name__ == "__main__":
    main()


# Optimized solution
import sys
input = sys.stdin.readline

def solve_e(n, a_list):
    days = 0
    ind_list = [0] * n
    match_count = 0
    queue = list(range(n))
    stack = dict()
    while len(queue) > 0:
        days += 1
        new_queue = []
        for p in queue:
            if ind_list[p] < n - 1:
                q = a_list[p][ind_list[p]] - 1
                k = str(min(p, q)) + "_" + str(max(p, q))
                if k in list(stack.keys()):
                    ind_list[p] += 1
                    ind_list[q] += 1
                    # print(days, p, q)
                    new_queue.append(p)
                    new_queue.append(q)
                    match_count += 1
                else:
                    stack[k] = 1
        queue = new_queue
    if match_count == n * (n - 1) // 2:
        return days - 1
    else:
        return -1


def test():
    N = 1000
    A_list = []
    for i in range(N):
        A_list.append(list(range(1, i + 1)) + list(range(i + 2, N + 1)))
    print((solve_e(N, A_list)))


def main():
    N = int(eval(input()))
    A_list = []
    for _ in range(N):
        A_list.append(list(map(int, input().split())))
    print((solve_e(N, A_list)))


if __name__ == "__main__":
    main()
# Original solution
from collections import deque
import copy

n = int(eval(input()))	
orders = [deque(list(map(int, input().split()))) for _ in range(n)]

cnt = 0
finished = set()
while True:
	impossible = True
	skip = copy.deepcopy(finished)
	#print(orders)
	for i in range(n):	
		if i not in skip and orders[i][0] - 1 not in skip and orders[orders[i][0] - 1][0] - 1 == i:				
			a = i
			b = orders[i][0] - 1
			impossible = False
			skip.add(a)
			skip.add(b)
			orders[orders[i][0] - 1].popleft()
			orders[i].popleft()

			if len(orders[i]) == 0:
				finished.add(a)
			if len(orders[b]) == 0:
				finished.add(b)
	cnt += 1

	if len(finished) == n:
		print(cnt)
		break

	if impossible:
		print((-1))
		break

# Optimized solution
from collections import deque

n = int(eval(input()))
orders = [deque([x - 1 for x in list(map(int, input().split()))] + [-1]) for _ in range(n)]

nxt = [orders[i].popleft() for i in range(n)]
days = [0 for _ in range(n)]

q = deque([i for i in range(n)])
while q:
	a = q.popleft()
	b = nxt[a]
	if nxt[nxt[a]] == a:
		days[a], days[b] = [max(days[a], days[b]) + 1 for _ in range(2)]
		nxt[a] = orders[a].popleft()
		nxt[b] = orders[b].popleft()
		q.append(a)
		q.append(b)

if sum(nxt) == -n:
	print((max(days)))
else:
	print((-1))
# Original solution
import sys
import copy
n=int(eval(input()))
maxmatch=n*(n-1)
a=[]
for i in range(n):
  a.append(list(map(int,input().split())))
day=0

match=[0]*(n+1)
jyunban=[i for i in range(n)]
jyunban_n=[]

while match[n]<maxmatch:
  jyunban_n.clear()
  day+=1
  check=[True]*(n+1)
  for i in jyunban:
    if match[i]==n-1 or check[i]==False:
      continue
    else:
      vs=a[i][match[i]]-1
      if check[i] and check[vs]:
        if  a[i][match[i]]-1==vs and a[vs][match[vs]]-1==i:
          match[i]+=1
          match[vs]+=1
          match[n]+=2
          check[i]=False
          check[vs]=False
          check[n]=False
          jyunban_n.append(i)
          jyunban_n.append(vs)
      
    if i==jyunban[-1]:
      if check[n]:
        print((-1))
        sys.exit()
  jyunban=copy.copy(jyunban_n)
        
print(day)


# Optimized solution
import sys
MAX_INT = int(10e9)
MIN_NUM = -MAX_INT
mod = 1000000007
sys.setrecursionlimit(1000000000)
def IL(): return list(map(int,input().split()))
def SL(): return input().split()
def I(): return int(sys.stdin.readline())
def S(): return eval(input())
 
N = I()
a = [IL()[::-1] for i in range(N)]
 
used = [-1]*N
updatelist = [i for i in range(N)]
total = N*(N-1)//2
cnt = 0
days = 0
ul = []
while updatelist:
  ul = []
  for i in updatelist:
    #print(a)
    #print(i+1)
    if len(a[i]) > 0 and used[i] != days:
      numIND = a[i][-1] -1
      #print(numIND+1)
      if a[numIND][-1] == i+1 and used[numIND] != days:
        a[i].pop(-1)
        a[numIND].pop(-1)
        used[i] = days
        used[numIND] = days
        ul.append(i)
        ul.append(numIND)
        cnt += 1
  else:
    updatelist = ul[:]
    if len(ul) != 0:
      days += 1
#print(a)
#print(cnt)
if cnt == total:
  print(days)
else:
  print((-1))
# Original solution
import sys
import copy
n=int(eval(input()))
a=[]
for i in range(n):
  a.append(list(map(int,input().split())))
maxmatch=n*(n-1)
day=0
q=[i for i in range(n)]
nq=[]
match=[0]*(n+1)
check=[0]*(n+1)
while q:
  day+=1
  for i in q:
    if match[i]==n-1 or check[i]==day:
      continue
    else:
      vs=a[i][match[i]]-1
      if check[vs]!=day and check[i]!=day and a[vs][match[vs]]-1==i and a[i][match[i]]-1==vs:
        match[i]+=1
        match[vs]+=1
        match[n]+=2
        check[i]=day
        check[vs]=day
        check[n]=day
        nq.append(i)
        nq.append(vs)
      
    if i==q[-1]:
      if check[n]!=day:
        print((-1))
        sys.exit()
  if match[n]==maxmatch:
    break
  q=copy.copy(nq)
  nq=[]
        
print(day)


# Optimized solution
import sys
n=int(eval(input()))
a=[]
for i in range(n):
  a.append(list(map(int,input().split())))
maxmatch=n*(n-1)
day=0
q=[i for i in range(n)]
nq=[]
match=[0]*(n+1)
check=[0]*(n+1)
while q:
  day+=1
  for i in q:
    if match[i]==n-1 or check[i]==day:
      continue
    else:
      vs=a[i][match[i]]-1
      if check[vs]!=day and check[i]!=day and a[vs][match[vs]]-1==i and a[i][match[i]]-1==vs:
        match[i]+=1
        match[vs]+=1
        match[n]+=2
        check[i]=day
        check[vs]=day
        check[n]=day
        nq.append(i)
        nq.append(vs)
      
    if i==q[-1]:
      if check[n]!=day:
        print((-1))
        sys.exit()
  if match[n]==maxmatch:
    break
  q=nq[:]
  nq=[]
        
print(day)
# Original solution
N = int(eval(input()))
A = [[x-1 for x in list(map(int, input().split()))[::-1]] for _ in range(N)]

def can_match(i, A, next_set):
  if not A[i]:
    return
  j = A[i][-1]
  if A[j][-1] == i:
    if i < j:
      next_set.add((i,j))
    else:
      next_set.add((j,i))
      
next_set = set()
for i in range(N):
  can_match(i, A, next_set)
  
day = 0
battle = 0
while next_set:
  day += 1
  current_set, next_set = next_set.copy(), set()
  for match in current_set:
    battle += 1
    del A[match[0]][-1]
    can_match(match[0], A, next_set)
    del A[match[1]][-1]
    can_match(match[1], A, next_set)
    
if battle == N*(N-1)//2:
  print(day)
else:
  print((-1))

# Optimized solution
N = int(eval(input()))
A = [[x-1 for x in list(map(int, input().split()))[::-1]] for _ in range(N)]

def can_match(i, A, next_set):
  if not A[i]:
    return
  j = A[i][-1]
  if A[j][-1] == i:
    if i < j:
      next_set.add((i,j))
    else:
      next_set.add((j,i))
      
next_set = set()
for i in range(N):
  can_match(i, A, next_set)
  
day = 0
battle = 0
while next_set:
  day += 1
  current_set, next_set = next_set, set()
  for match in current_set:
    battle += 1
    del A[match[0]][-1]
    can_match(match[0], A, next_set)
    del A[match[1]][-1]
    can_match(match[1], A, next_set)
    
if battle == N*(N-1)//2:
  print(day)
else:
  print((-1))
# Original solution
N = int(eval(input()))
A = [[x-1 for x in list(map(int, input().split()))[::-1]] for _ in range(N)]

def can_match(i, A, next_set):
  if not A[i]:
    return
  j = A[i][-1]
  if A[j][-1] == i:
    if i < j:
      next_set.add((i,j))
    else:
      next_set.add((j,i))
      
next_set = set()
for i in range(N):
  can_match(i, A, next_set)
  
day = 0
battle = 0
while next_set:
  day += 1
  current_set, next_set = next_set, set()
  for match in current_set:
    battle += 1
    del A[match[0]][-1]
    can_match(match[0], A, next_set)
    del A[match[1]][-1]
    can_match(match[1], A, next_set)
    
if battle == N*(N-1)//2:
  print(day)
else:
  print((-1))

# Optimized solution
import sys
input = sys.stdin.readline
N = int(eval(input()))
A = [[x-1 for x in list(map(int, input().split()))[::-1]] for _ in range(N)]

def can_match(i, A, next_set):
  if not A[i]:
    return
  j = A[i][-1]
  if A[j][-1] == i:
    if i < j:
      next_set.add((i,j))
    else:
      next_set.add((j,i))
      
next_set = set()
for i in range(N):
  can_match(i, A, next_set)
  
day = 0
battle = 0
while next_set:
  day += 1
  current_set, next_set = next_set, set()
  for match in current_set:
    battle += 1
    del A[match[0]][-1]
    can_match(match[0], A, next_set)
    del A[match[1]][-1]
    can_match(match[1], A, next_set)
    
if battle == N*(N-1)//2:
  print(day)
else:
  print((-1))
# Original solution
def solve():
  ans = 0
  N = int(eval(input()))
  stacks = [list([int(x)-1 for x in input().split()])[::-1] for _ in range(N)]
  lis = [0]*N
  cnt = 0
  now = 0
  flag = 0
  while cnt<N*(N-1)//2:
    while not stacks[now]:
      now = (now+1)%N
    a = stacks[now][-1]
    while not stacks[a]:
      now = (now+1)%N
      a = stacks[now][-1]
    if stacks[a][-1] == now:
      lis[now] = max(lis[now],lis[a])+1
      lis[a] = lis[now]
      stacks[a].pop(-1)
      stacks[now].pop(-1)
      cnt += 1
      flag = 0
    else:
      now = a
      flag += 1
    if flag==2*N:
      return -1
  ans = max(lis)
  return ans
print((solve()))

# Optimized solution
def solve():
  ans = 0
  N = int(eval(input()))
  stacks = [list([int(x)-1 for x in input().split()])[::-1] for _ in range(N)]
  lis = [0]*N
  cnt = 0
  now = 0
  flag = 0
  while cnt<N*(N-1)//2:
    while not stacks[now]:
      now = (now+1)%N
    a = stacks[now][-1]
    if not stacks[a]:
      return -1
    if stacks[a][-1] == now:
      lis[now] = max(lis[now],lis[a])+1
      lis[a] = lis[now]
      stacks[a].pop(-1)
      stacks[now].pop(-1)
      cnt += 1
      flag = 0
    else:
      now = a
      flag += 1
    if flag==N:
      return -1
  ans = max(lis)
  return ans
print((solve()))
# Original solution
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

n = int(readline())
a = [list(map(int, readline().split())) for _ in range(n)]
for cnt in range(n ** 2):
    check = []
    flag = True
    for i in range(n):
        if a[i]:
            flag = False
            if a[a[i][0] - 1][0] == i + 1:
                check.append(i)
    if flag:
        print(cnt)
        break
    if check:
        for v in check:
            a[v].pop(0)
    else:
        print((-1))
        break


# Optimized solution
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

n = int(readline())
a = [list(map(int, readline().split())) for _ in range(n)]
q = list(range(n))
for cnt in range(1, n ** 2 + 2):
    qq = set()
    while q:
        x = q.pop()
        if a[a[x][0] - 1][0] == x + 1:
            qq.add(x)
            qq.add(a[x][0] - 1)
    if qq:
        for x in qq:
            a[x].pop(0)
            if a[x]:
                q.append(x)
    else:
        print((-1))
        break
    if not q:
        print(cnt)
        break
# Original solution
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

n = int(readline())
a = [list([int(x) - 1 for x in readline().split()]) for _ in range(n)]
q = list(range(n))
cnt = 0
while q:
    cnt += 1
    qq = set()
    while q:
        x = q.pop()
        if a[a[x][0]][0] == x:
            qq.add(x)
            qq.add(a[x][0])
    if qq:
        for x in qq:
            a[x].pop(0)
            if a[x]:
                q.append(x)
    else:
        print((-1))
        exit()
print(cnt)


# Optimized solution
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

n = int(readline())
a = [list([int(x) - 1 for x in readline().split()]) for _ in range(n)]
q = list(range(n))
for cnt in range(1, n ** 2):
    qq = set()
    for x in q:
        if a[a[x][0]][0] == x:
            qq.add(x)
            qq.add(a[x][0])
    if qq:
        q = []
        for x in qq:
            a[x].pop(0)
            if a[x]:
                q.append(x)
    else:
        print((-1))
        break
    if not q:
        print(cnt)
        break
# Original solution
import sys
input = sys.stdin.readline
n = int(eval(input()))
a = [list(map(int, input().split())) for _ in range(n)]
ans = 0
r = set(list(range(n)))
N = n*(n-1) // 2 + 1
for _ in range(N):
    if not r:
        print(_)
        break
    ne = set()
    flag = True
    for j in r:
        if not a[j]:
            continue
        c = a[j][0]
        if c == "-":
            continue
        if j + 1 == a[c-1][0]:
            a[j][0] = "-"
            a[c-1][0] = "-"
            ne.add(j)
            ne.add(c-1)
    for j in list(ne):
        if a[j]:
            if a[j][0] == "-":
                a[j] = a[j][1:]
                flag = False
                if not a[j]:
                    ne.remove(j)
    if flag:
        print((-1))
        break
    else:
        r = ne


# Optimized solution
import sys
input = sys.stdin.readline
n = int(eval(input()))
a = [list(map(int, input().split())) for _ in range(n)]
ans = 0
r = set(list(range(n)))
N = n*(n-1) // 2 + 1
for _ in range(N):
    if not r:
        print(_)
        break
    ne = set()
    flag = True
    for j in r:
        if not a[j]:
            continue
        c = a[j][0]
        if c == "-":
            continue
        if j + 1 == a[c-1][0]:
            a[j][0] = "-"
            a[c-1][0] = "-"
            ne.add(j)
            ne.add(c-1)
    for j in list(ne):
        if a[j]:
            if a[j][0] == "-":
                a[j].pop(0)
                flag = False
                if not a[j]:
                    ne.remove(j)
    if flag:
        print((-1))
        break
    else:
        r = ne
# Original solution
from collections import deque
import sys
input = lambda: sys.stdin.readline()[:-1]
n=int(eval(input()))
data=[deque(list(map(int,input().split()))) for i in range(n)]
last=n*(n-1)
count=0
while last:
	flag=1
	count+=1
	taisenzumi=[0]*n
	for i in range(n):
		if data[i]:
			aite=data[i][0]
			if data[aite-1][0]==i+1:
				if taisenzumi[i]:continue
				if taisenzumi[aite-1]:continue				
				
				data[i].popleft()
				data[aite-1].popleft()
				taisenzumi[aite-1]=1
				taisenzumi[i]=1
				last-=2
				flag=0
			else:continue
	if flag:
		break
else:
	print(count)
	exit()
print((-1))




# Optimized solution
import sys
sys.setrecursionlimit(2147483647)
INF=float("inf")
MOD=10**9+7
input=lambda:sys.stdin.readline().rstrip()
def resolve():
    n=int(eval(input()))
    M=[None]*n
    for i in range(n):
        M[i]=list([int(x)-1 for x in input().split()])[::-1]

    # i が誰かしらと対戦できるか
    def check(i):
        if(not M[i]): # 既に試合を終えている
            return False
        j=M[i][-1]
        if(not M[j]): # これは起こり得ない
            return False
        return i==M[j][-1]

    # 初日に対戦できる人をピックアップ
    # 重複が起こるが、後で unique を取る
    Q=[]
    for i in range(n):
        if(check(i)):
            j=M[i][-1]
            if(i>j): i,j=j,i # i<j
            Q.append((i,j))

    # 処理を行なっていく
    day=0
    nQ=[] # 次の試合相手
    while(Q):
        # Q には重複があるので unique
        Q=list(set(Q))
        # 先に全ての試合を終わらせる必要がある
        for i,j in Q:
            M[i].pop(); M[j].pop()
        # 試合を終えた人は次の試合を行える可能性がある
        for i,j in Q:
            if(check(i)):
                k=M[i][-1]
                nQ.append((min(i,k),max(i,k)))
            if(check(j)):
                k=M[j][-1]
                nQ.append((min(j,k),max(j,k)))
        Q,nQ=nQ,[]
        day+=1

    print((day if(all(M[i]==[] for i in range(n))) else "-1"))
resolve()
# Original solution
from collections import deque

def main():    
    nums = {}
    N = int(eval(input()))
    count = 0
    for i in range(1, N+1):
        for j in range(i+1, N+1):
            nums[(i, j)] = count
            count += 1
    
    graph = {i:deque() for i in range(count)}
    input_num = [0] * count
    
    for i in range(1, N+1):
        A = list(map(int, input().split()))
    
        for j in range(N-2):
            a, b = i, A[j]
            if a > b: a, b = b, a
            
            c, d = i, A[j+1]
            if c > d: c, d = d, c
        
            n = nums[(c, d)]        
            graph[nums[(a, b)]].append(n)
            input_num[n] += 1
        
    q = deque([(i, 1) for i in range(count) if not input_num[i]])
    size = len(q)
    dist = [0] * count
    
    while q:
        v, c = q.popleft()
        c += 1
        for u in graph[v]:
            input_num[u] -= 1
            dist[u] = max(dist[u], c)
            if not input_num[u]:
                q.append((u, c))
                size += 1
    
    if size != count: ans = -1
    else: ans = max(dist)
    
    print(ans)

if __name__ == '__main__':
    main()


# Optimized solution
import sys

input = sys.stdin.readline

def main():
    N = int(eval(input()))
    
    Id = {}
    
    cur = 0
    for i in range(1, N+1):
        for j in range(i+1, N+1):
            Id[(i,j)] = cur
            cur += 1
            
    G = [[] for i in range(N*(N-1)//2)]
    size = [0] * (N*(N-1)//2)
    
    for i in range(1, N+1):
        for idx, j in enumerate(list(map(int, input().split()))):
            if i < j: k = Id[(i, j)]
            else: k = Id[(j, i)]
            if idx: 
                G[par].append(k)
                size[k] += 1
            par = k
            
    g = [idx for idx, s in enumerate(size) if s == 0]
    
    ans = 0
    while g:
        ans += 1
        n_g = []
        
        for v in g:
            length = len(G[v])
            if not length: continue
            
            size[G[v][0]] -= 1
            if not size[G[v][0]]: n_g.append(G[v][0])
    
            if length == 2:
                size[G[v][1]] -= 1
                if not size[G[v][1]]: n_g.append(G[v][1])
        g = n_g
        
    for s in size:
        if s != 0:
            print((-1))
            sys.exit()
    print(ans)
            
if __name__ == '__main__':
    main()