//#pragma GCC optimize("O3", "unroll-loops")
//#pragma GCC target("avx2")
#include<bits/stdc++.h>

#define FAST ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define FIXED cout << fixed << setprecision(12)
#define RANDOM srand(94385)
#define all(a) a.begin(), a.end()
#define shuffle(a) \
    for (int i = 0; i < sz(a); ++i) \
        swap(a[i], a[rand() % sz(a)]);
#define enter putchar('\n')
#define space putchar(' ')
#define Mem(a, x) memset(a, x, sizeof(a))
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;

inline ll read() {
    ll x = 0;
    int f = 0;
    char ch = getchar();
    while (ch < '0' || ch > '9') f |= (ch == '-'), ch = getchar();
    while (ch >= '0' && ch <= '9') x = (x << 3) + (x << 1) + ch - '0', ch = getchar();
    return x = f ? -x : x;
}

inline void write(ll x) {
    if (x == 0) {
        putchar('0');
        return;
    }
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    static char s[23];
    int l = 0;
    while (x != 0)s[l++] = x % 10 + 48, x /= 10;
    while (l)putchar(s[--l]);
}

int lowbit(int x) { return x & (-x); }

template<class T>
T big(const T &a1, const T &a2) { return a1 > a2 ? a1 : a2; }

template<typename T, typename ...R>
T big(const T &f, const R &...r) { return big(f, big(r...)); }

template<class T>
T sml(const T &a1, const T &a2) { return a1 < a2 ? a1 : a2; }

template<typename T, typename ...R>
T sml(const T &f, const R &...r) { return sml(f, sml(r...)); }

template<class T, class U>
inline void checkMin(T &x, U y) { if (y < x) x = y; }

template<class T, class U>
inline void checkMax(T &x, U y) { if (y > x) x = y; }

template<class T, class U>
inline bool ifMax(T &x, U y) {
    if (y > x) return x = y, true;
    return false;
}

template<class T, class U>
inline bool ifMin(T &x, U y) {
    if (y < x) return x = y, true;
    return false;
}

const int M = 1123456;// 2e5+5
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1000000007;// 1e9+7

// HAVE FREE OPEN IN MAIN FUNCTION

int n;
vector<int> to[M];
int fa[M];
int inDg[M];
set<int> points;
int cnt = 0;

void dfs(int now) {
    cnt++;
    for (auto son:to[now]) {
        inDg[son]--;
        if (inDg[son] == 0) {
            dfs(son);
        }
    }
}

int dp[M];


int dfs2(int now) {
    if (dp[now] != -1)
        return dp[now];
    int tmp = 0;
    for (auto son:to[now]) {
        checkMax(tmp, dfs2(son) + 1);
    }
    return dp[now] = tmp;
}


void init() {
    Mem(dp, -1);
    n = read();
    for (int i = 1; i <= n; ++i) {
        int bf = 0;
        points.insert(0);
        for (int j = 1; j < n; ++j) {
            int tmp1 = read();
            int tmp2 = i;
            if (tmp1 > tmp2)swap(tmp1, tmp2);
            int tmp = tmp1 * 1000 + tmp2;
            points.insert(tmp);
            fa[tmp] = bf;
            to[bf].emplace_back(tmp);
            inDg[tmp]++;
            bf = tmp;
        }
    }
    dfs(0);
    if (cnt < points.size()) {
        puts("-1");
        return;
    }
    write(dfs2(0)), enter;
}

void solve() {

}

int main() {
//#ifndef ONLINE_JUDGE
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);
//#endif
    init();

    solve();

    return 0;
}

Measured memory_bytes: 78848