#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int f;
	cin >> f;
	bool ans = true;
	while (f--) {
		int t, n;
		cin >> t >> n;
		vector<char> dp(t + 1, 1);
		while (n--) {
			int l, r;
			cin >> l >> r;
			int len = r - l;
			vector<char> ndp(t + 1);
			FOR(j, 0, t + 1) {
				if (j + len <= t) {
					ndp[j + len] |= dp[j];
				}
				if (j - len >= 0) {
					ndp[j - len] |= dp[j];
				}
			}
			dp = ndp;
		}
		ans &= accumulate(ALL(dp), 0) != 0;
	}
	if (!ans) {
		cout << "im";
	}
	cout << "possible\n";
	return 0;
}