#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

const int maxn = 300;

vector <int> G[maxn];

int k, n;

int del[maxn];
int h[maxn];
int cnt = 0;

int main() {
    scanf("%d%d", &k, &n);
    if (n >= 10 * k) {
        printf("possible");
        return 0;
    }

    for (int i = 0; i < n; ++i) {
        int d;
        scanf("%d", &d);
        G[i].resize(d);
        for (int j = 0; j < d; ++j) {
            scanf("%d", &G[i][j]);
            --G[i][j];
        }
    }

    while (true) {
        int v = -1;
        for (int i = 0; i < n; ++i) {
            h[i] = 0;
            for (int j = 0; j < (int)G[i].size(); ++j) {
                int u = G[i][j];
                if (del[u] == 0) ++h[i];
            }
            if (del[i] == 0 && (v == -1 || h[v] > h[i])) {
                v = i;
            }
        }
        if (v == -1) break;
        ++cnt;
        del[v] = 1;
        for (int j = 0; j < (int)G[v].size(); ++j) {
            del[G[v][j]] = 1;
        }
    }
    if (cnt >= k) {
        printf("possible");
    } else {
        printf("impossible");
    }
}