// @EXPECTED_RESULTS@: TIME_LIMIT_EXCEEDED, WRONG_ANSWER
import kotlin.math.max

fun main() {
    val (n, r) = readln().split(" ").map { it.toInt() }
    val minScore = .5 * r * n * (3 * n + 1)
    val ranking =
        System.`in`.bufferedReader().lineSequence().take(r).map { line -> line.split(" ").map { it.toInt() } }.toList()
    // optimal ranking for a conest if ordered by score
    // (2n, 1), (2n-1, 2), ..., (2n -i, i+1), ... (n+1, n)
    // Only consider optimal pairs for a contest
    val options = ranking.distinct()
        .map { order ->
            val ranks = order.withIndex().sortedBy { it.value }
            (0 until n).map { ranks[it].index to ranks[2 * n - it - 1].index }
        }
    options
        .map { option ->
            ranking.sumOf { ranks ->
                option.sumOf { (a, b) -> max(ranks[a], ranks[b]) }
            }
        }
        .firstOrNull { it >= minScore }?.also { println("possible") } ?: println("impossible")
}