#include <cassert>
#include <functional>
#include <iostream>
#include <vector>

using namespace std;

int main() {
	int n, r;
	cin >> n >> r;
	vector<vector<int>> scores(r, vector<int>(2 * n));
	for(auto& v : scores)
		for(auto& x : v) cin >> x;
	vector<int> left, right;
	for(int i = 0; i < 2 * n; ++i) {
		if(scores[0][i] > n)
			left.push_back(i);
		else
			right.push_back(i);
	}
	assert(left.size() == n);
	assert(right.size() == n);
	vector<vector<bool>> g(n, vector<bool>(n));
	for(int i = 0; i < n; ++i) {
		for(int j = 0; j < n; ++j) {
			bool ok = true;
			for(int k = 0; k < r; ++k) {
				if((scores[k][left[i]] > n) + (scores[k][right[j]] > n) != 1) {
					ok = false;
					break;
				}
			}
			g[i][j] = ok;
		}
	}

	vector<int> mt(n, -1);
	vector<bool> used;
	function<bool(int)> dfs;
	long long ops = 0;
	dfs           = [&](int v) -> bool {
        if(used[v]) return false;
        used[v] = true;
        for(int i = 0; i < n; ++i) {
            ops += 1;
            if(!g[v][i]) continue;
            if(mt[i] == -1 || dfs(mt[i])) {
                mt[i] = v;
                return true;
            }
        }
        return false;
	};
	for(int i = 0; i < n; ++i) {
		used.assign(n, false);
		if(!dfs(i)) {
			cout << "impossible" << endl;
			cerr << "ops: " << ops << endl;
			return 0;
		}
	}
	cout << "possible" << endl;
	cerr << "ops: " << ops << endl;
}