#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
typedef long long ll;
typedef long double ld;
using namespace std;
const int N = 1e3 + 5;
int n, h;
map<int, int> mp;
priority_queue<pair<int, int>> q;
int main() {
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n >> h;
    for(int i = 0;i < n;i++) {
		int x;
		cin >> x;
		mp[x]++;
	}
	for(auto i : mp)
		q.push({i.second, i.first});
	bool ok = false;
	while(1) {
		vector<int> tmp;
		for(int i = 0;i < h && q.size();i++) {
			auto cur = q.top();
			q.pop();
			tmp.push_back(cur.second);
		}
		if(tmp.size() < h)
			break;
		ok = true;
		for(auto i : tmp) {
			cout << i << " ";
			mp[i]--;
			if(mp[i])
				q.push({mp[i], i});
		}
		cout << '\n';
	}
	if(!ok)
		cout << "impossible";
    return 0;
}