#include <cstdio>
#include <cstdlib>
#include <map>
#include <set>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;


const int N = 10000;
int k, ok;
int a[N], b[N], beg[N*2], end[N*2];
int u[N], p[N*2];

void dfs(int v, int U = 1) {
    u[v] = U;
    for (int i = p[a[v]+1]; i < b[v] && ok; i = p[i+1])
        if (beg[i]+1) {
            if (b[beg[i]] < b[v])
                continue;
            if (u[beg[i]] && u[beg[i]] == u[v]) {
                ok = 0;
                return;
            }else if(!u[beg[i]])
                dfs(beg[i], U*-1);
        } else if (end[i]+1) {
            if (a[end[i]] > a[v])
                continue;
            if (u[end[i]] && u[end[i]] == u[v]) {
                ok = 0;
                return;
            } else if(!u[end[i]])
                dfs(end[i], U*-1);
        }
}

void solve() {
    if (!k)return;
    memset(beg, -1, sizeof beg);
    memset(end, -1, sizeof end);
    memset(u, 0, sizeof u);

    for (int i = 0; i <= k*2; i++)
        p[i] = i;

    for (int i = 0; i < k; i++) {
        //scanf("%d%d", a+i, b+i);
        if (a[i] > b[i])
            swap(a[i], b[i]);
        beg[a[i]] = i;
        end[b[i]] = i;
    }

    for (int i = k*2; i > 0; i--)
        if (beg[i-1]==-1&&end[i-1]==-1)
            p[i-1]=p[i];
    ok = 1;
    for (int i = 0; ok && i < k; i++)
        if (!u[i])
            dfs(i);
    if (!ok)printf("im");
    puts("possible");
}

int main() {

  freopen("dna.in", "r", stdin);
  freopen("dna.out", "w", stdout);
    //while(~scanf("%d", &k))
        //solve();
  k = 10000;
  int i = 0;
  for (int l = 0, r = k - k / 4 - 1; l < k / 4; l++, r--)
  {
    a[i] = l;
    b[i++] = r;
  }
  for (int l = k / 4, r = k - 1; l < k / 2; l++, r--)
  {
    a[i] = l;
    b[i++] = r;
  }
  //cout << i << endl;
  for (int i = 0; i < 128; i++)
    solve();
    return 0;
}