#include <iostream>
#include <vector>

using namespace std;

bool knows_any(const vector<vector<bool>> &knows, const int i)
{
    const int n = knows.size();

    for (int j = 0; j < i; j++) {
        if (knows[i][j]) {
            return true;
        }
    }

    return false;
}

bool known_by_all(const vector<vector<bool>> &knows, const int i)
{
    for (int j = 0; j < i; j++) {
        if (!knows[j][i]) {
            return false;
        }
    }

    return true;
}

int superstar(const vector<vector<bool>> &knows, const int n)
{
    if (n == 1) return 1;

    int star = superstar(knows, n - 1);

    if (star != -1 && knows[n - 1][star] && !knows[star][n - 1]) {
        return star;
    }

    if (known_by_all(knows, n - 1) && !knows_any(knows, n - 1)) {
        return n - 1;
    }

    return -1;
}

int superstar(const vector<vector<bool>> &knows)
{
    const int n = knows.size();

    int i = 0;
    for (int j = 1; j < n; j++) {
        if (knows[i][j] || !knows[j][i]) {
            i = j;
        }
    }

    if (known_by_all(knows, i) && !knows_any(knows, i)) {
        return i;
    }
    
    return -1;
}

int main(void)
{
    int n;
    cin >> n;

    vector<vector<bool>> knows(n, vector<bool>(n));

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            bool b;
            cin >> b;
            knows[i][j] = b;
        }
    }

    cout << superstar(knows) << endl;

    return 0;
}