#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const int N = 1000006;

int h, f[N];
vector<pair<int, int>> v;

bool check(int p) {
    vector<vector<int>> vs(p);
    int i = 0;
    for (; i < (int) v.size() and v[i].first >= p; ++i)
        for (auto &hand : vs)
            hand.push_back(v[i].second);
    for (int j = 0; i < (int) v.size(); ++i) {
        int cnt = v[i].first, val = v[i].second;
        while (cnt--) {
            vs[j].push_back(val);
            j = (j + 1) % p;
        }
    }
    for (const auto &hand : vs)
        if (hand.size() < h)
            return false;
    return true;
}

int main() {
    ios::sync_with_stdio(false); cout.tie(nullptr); cin.tie(nullptr);
    int n;
    cin >> n >> h;
    for (int i = 0; i < n; ++i) {
        int x; cin >> x;
        if (f[x] == 0)
            v.emplace_back(0, x);
        ++f[x];
    }
    for (auto &p : v)
        p.first = f[p.second];
    sort(v.rbegin(), v.rend());
    int l = 1, r = n, ans = -1;
    while (l <= r) {
        int m = (l + r) / 2;
        if (check(m)) {
            ans = m; l = m + 1;
        } else r = m - 1;
    }
    if (ans == -1) {
        cout << "impossible\n"; return 0;
    }
//    cerr << ans << '\n';
    vector<vector<int>> vs(ans);
    int i = 0;
    for (; i < (int) v.size() and v[i].first >= ans; ++i)
        for (auto &hand : vs)
            hand.push_back(v[i].second);
    for (int j = 0; i < (int) v.size(); ++i) {
        int cnt = v[i].first, val = v[i].second;
        while (cnt--) {
            vs[j].push_back(val);
            j = (j + 1) % ans;
        }
    }
    for (const auto &hand : vs) {
        assert(hand.size() >= h);
        for (int c = 0; c < h; ++c)
            cout << hand[c] << ' ';
        cout << '\n';
    }
    return 0;
}