def examA():
    N = I()
    ans = 0
    print(ans)
    return

def examB():
    ans = 0
    print(ans)
    return

def examC():
    ans = 0
    print(ans)
    return

def examD():
    ans = 0
    print(ans)
    return

def examE():
    # http://zehnpaard.hatenablog.com/entry/2018/06/26/201512
    # トポロジカルソート
    def topological_sort(n,outs,ins):
        q = deque(v1 for v1 in range(n) if ins[v1] == 0)
        res = []
        cur = 0
        while q and cur<n+1:
            cur += 1
            v1 = q.popleft()
            res.append(v1)
            for v2 in outs[v1]:
                ins[v2] -= 1
                if ins[v2] == 0:
                    q.append(v2)
        if q:
            return []
        return res

    def dfs(n, e, edges):
        result = 0
        for i in edges[e]:
            t = dfs(n, i, edges)
            if t > result:
                result = t
        result += 1
        return result

    N = I()
    node = N*(N-1)//2
    V = [[]for _ in range(node)]
    A = [LI() for _ in range(N)]
    D = defaultdict(int)
    cur = 0
    for i in range(N):
        for j in range(i+1,N):
            D[(i,j)] = cur
            D[(j,i)] = cur
            cur += 1
    ins = [0]*node
    for i in range(N):
        a = A[i]
        for j in range(N-2):
            fr = D[(i,a[j]-1)]
            to = D[(i,a[j+1]-1)]
            #print(fr,to)
            V[fr].append(to)
            ins[to] += 1
    #print(V)
    #print(ins)
    Order = topological_sort(node, V, ins)
    #print(Order)
    if not Order:
        print(-1)
        return
    start = Order.index(0)
    ans = dfs(node,start,V)
    print(ans)
    return

def examF():
    ans = 0
    print(ans)
    return

import sys,copy,bisect,itertools,heapq,math,random
from heapq import heappop,heappush,heapify
from collections import Counter,defaultdict,deque
def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LSI(): return list(map(str,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def SI(): return sys.stdin.readline().strip()
global mod,mod2,inf,alphabet,_ep
mod = 10**9 + 7
mod2 = 998244353
inf = 10**18
_ep = 10**(-12)
alphabet = [chr(ord('a') + i) for i in range(26)]

if __name__ == '__main__':
    examE()

"""

"""

### FIXED CODE ###

def examA():
    N = I()
    ans = 0
    print(ans)
    return

def examB():
    ans = 0
    print(ans)
    return

def examC():
    ans = 0
    print(ans)
    return

def examD():
    ans = 0
    print(ans)
    return

def examE():
    N = I()
    node = N*(N-1)//2
    V = [[]for _ in range(node)]
    D = [[0]*N for _ in range(N)]
    cur = 0
    for i in range(N):
        for j in range(i+1,N):
            D[i][j] = cur
            D[j][i] = cur
            cur += 1
    #A = [LI() for _ in range(N)]
    for i in range(N):
        a = LI()
        for j in range(N-2):
            fr = D[i][a[j]-1]
            to = D[i][a[j+1]-1]
            #print(fr,to)
            V[fr].append(to)

    visited = [False] * node
    calculated = [False] * node
    dp = [1] * node
    # https://mhiro216.hatenablog.com/entry/2019/09/08/142414
    def dfs(v):
        if visited[v]:
            if not calculated[v]:
                return -1  # 計算が終わっていない頂点を2度訪れるのはループがあるということ
            return dp[v]
        visited[v] = True
        for u in V[v]:  # 全ての辺をなめる
            res = dfs(u)
            if res == -1: return -1  # ループがあれば-1を返す
            elif res+1>dp[v]:
                dp[v] = res + 1
        calculated[v] = True
        return dp[v]

    ans = 0
    for i in range(node):
        res = dfs(i)
        ans = max(ans,res)
        if res == -1:
            print('-1')  # ループがあれば-1を返す（問題文の指示）
            return
    print(ans)
    return

def examF():
    ans = 0
    print(ans)
    return

import sys,copy,bisect,itertools,heapq,math,random
from heapq import heappop,heappush,heapify
from collections import Counter,defaultdict,deque
def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LSI(): return list(map(str,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def SI(): return sys.stdin.readline().strip()
global mod,mod2,inf,alphabet,_ep
mod = 10**9 + 7
mod2 = 998244353
inf = 10**18
_ep = 10**(-12)
alphabet = [chr(ord('a') + i) for i in range(26)]

sys.setrecursionlimit(10**6)

if __name__ == '__main__':
    examE()

"""

"""