# Original solution
# -*- coding: utf-8 -*-
import sys
import math
from bisect import bisect_left
from bisect import bisect_right
import collections
import copy
import heapq
from collections import defaultdict
from heapq import heappop, heappush
import itertools
input = sys.stdin.readline

##### リストの 二分木検索 #####
# bisect_left(lists, 3)
# bisect_right(lists, 3)

##### プライオリティキュー #####
# heapq.heapify(a) #リストaのheap化
# heapq.heappush(a,x) #heap化されたリストaに要素xを追加
# heapq.heappop(a) #heap化されたリストaから最小値を削除＆その最小値を出力

# heapq.heappush(a, -x) #最大値を取り出す時は、pushする時にマイナスにして入れよう
# heapq.heappop(a) * (-1) #取り出す時は、-1を掛けて取り出すこと

##### タプルリストのソート #####
# sorted(ans) #(a, b) -> 1st : aの昇順, 2nd : bの昇順
# sorted(SP, key=lambda x:(x[0],-x[1])) #(a, b) -> 1st : aの昇順, 2nd : bの降順
# sorted(SP, key=lambda x:(-x[0],x[1])) #(a, b) -> 1st : aの降順, 2nd : bの昇順
# sorted(SP, key=lambda x:(-x[0],-x[1])) #(a, b) -> 1st : aの降順, 2nd : bの降順

# sorted(SP, key=lambda x:(x[1])) #(a, b) -> 1st : bの昇順
# sorted(SP, key=lambda x:(-x[1])) #(a, b) -> 1st : bの降順

def inputInt(): return int(eval(input()))
def inputMap(): return list(map(int, input().split()))
def inputList(): return list(map(int, input().split()))

def main():
	N = inputInt()
	A = []
	for i in range(N):
		tmp = inputList()
		A.append(tmp)

	ind = [0] * N
	ans = 0

	anfl = True

	for i in range(90000):
		flg = False
		doList = []

		for i, val in enumerate(ind):
			if val == -1:
				continue

			min = A[i]
			target = min[val]

			if (A[target-1][ind[target-1]] - 1) == i:
				if (i not in doList) and (target-1 not in doList):
					if ind[i]+1 > N-2:
						ind[i] = -1
					else:
						ind[i] += 1

					if ind[target-1]+1 > N-2:
						ind[target-1] = -1
					else:
						ind[target-1] += 1

					doList.append(i)
					doList.append(target-1)
					flg = True

		if flg == True:
			ans += 1
		else:
			anfl = False
			break

	if anfl == False:
		for i in ind:
			if i != -1:
				print((-1))
				sys.exit()

		print(ans)
	else:
		print(((N*(N-1))/2))



if __name__ == "__main__":
	main()


# Optimized solution
# -*- coding: utf-8 -*-
import sys
import math
from bisect import bisect_left
from bisect import bisect_right
import collections
import copy
import heapq
from collections import defaultdict
from heapq import heappop, heappush
import itertools
input = sys.stdin.readline

##### リストの 二分木検索 #####
# bisect_left(lists, 3)
# bisect_right(lists, 3)

##### プライオリティキュー #####
# heapq.heapify(a) #リストaのheap化
# heapq.heappush(a,x) #heap化されたリストaに要素xを追加
# heapq.heappop(a) #heap化されたリストaから最小値を削除＆その最小値を出力

# heapq.heappush(a, -x) #最大値を取り出す時は、pushする時にマイナスにして入れよう
# heapq.heappop(a) * (-1) #取り出す時は、-1を掛けて取り出すこと

##### タプルリストのソート #####
# sorted(ans) #(a, b) -> 1st : aの昇順, 2nd : bの昇順
# sorted(SP, key=lambda x:(x[0],-x[1])) #(a, b) -> 1st : aの昇順, 2nd : bの降順
# sorted(SP, key=lambda x:(-x[0],x[1])) #(a, b) -> 1st : aの降順, 2nd : bの昇順
# sorted(SP, key=lambda x:(-x[0],-x[1])) #(a, b) -> 1st : aの降順, 2nd : bの降順

# sorted(SP, key=lambda x:(x[1])) #(a, b) -> 1st : bの昇順
# sorted(SP, key=lambda x:(-x[1])) #(a, b) -> 1st : bの降順

def inputInt(): return int(eval(input()))
def inputMap(): return list(map(int, input().split()))
def inputList(): return list(map(int, input().split()))

def main():
	N = inputInt()
	A = []
	for i in range(N):
		tmp = inputList()
		A.append(tmp)

	ind = [0] * N
	ans = 0

	anfl = True

	for i in range(80000):
		flg = False
		doList = []

		for i, val in enumerate(ind):
			if val == -1:
				continue

			min = A[i]
			target = min[val]

			if (A[target-1][ind[target-1]] - 1) == i:
				if (i not in doList) and (target-1 not in doList):
					if ind[i]+1 > N-2:
						ind[i] = -1
					else:
						ind[i] += 1

					if ind[target-1]+1 > N-2:
						ind[target-1] = -1
					else:
						ind[target-1] += 1

					doList.append(i)
					doList.append(target-1)
					flg = True

		if flg == True:
			ans += 1
		else:
			anfl = False
			break

	if anfl == False:
		for i in ind:
			if i != -1:
				print((-1))
				sys.exit()

		print(ans)
	else:
		print(((N*(N-1))/2))



if __name__ == "__main__":
	main()