/* Problem URL: https://cses.fi/problemset/task/3359 */

#include <bits/stdc++.h>

using namespace std;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (int i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;

    V<string> fds(n);
    cin >> fds;

    string ans(2 * n - 1, 'Z' + 1);

    queue<pair<int, int>> q;
    V<V<bool>> vis(n, V<bool>(n, false));
    vis[0][0] = true;
    q.emplace(0, 0);
    queue<pair<int, int>> tmp;

    rep(_, n * 2 - 1) {
        while (!q.empty()) {
            auto [i, j] = q.front();
            q.pop();

            int pos = i + j;

            rmin(ans[pos], fds[i][j]);
            tmp.emplace(i, j);
        }

        while (!tmp.empty()) {
            auto [i, j] = tmp.front();
            tmp.pop();

            if (ans[i + j] < fds[i][j]) {
                continue;
            }

            int add[][2] = {{0, 1}, {1, 0}};

            for (auto &k : add) {
                int id = i + k[0];
                int jd = j + k[1];

                if (id < n && jd < n && !vis[id][jd]) {
                    vis[id][jd] = true;
                    q.emplace(id, jd);
                }
            }
        }
    }

    cout << ans << '\n';
}