#define taskname "K"
#include <bits/stdc++.h>
#define ii pair<int,int>
#define ff first
#define ss second

using namespace std;
const int maxn = 1e5 + 10;
vector<int> adj[maxn], adj2[maxn];
ii a[maxn];
int n, m, bn[maxn], col[maxn];

bool DFS(int u, int p = 0)
{
    if (col[u] == 0) col[u] = 1;
    for (int v: adj2[u]) if (v != p && col[v] < 2)
    {
        if (col[v] == 1) return 1;
        if (col[v] == 0 && DFS(v)) return 1;
    }
    col[u] = 2;
    return 0;
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    cin>>m>>n;
    for (int i=1; i<=m; i++)
    {
        cin>>a[i].ff>>a[i].ss;
        adj[a[i].ff].emplace_back(a[i].ss),
        adj[a[i].ss].emplace_back(a[i].ff);
    }
    for (int i=1; i<=n; i++)
        sort(adj[i].begin(), adj[i].end()),
        adj[i].resize(unique(adj[i].begin(), adj[i].end()) - adj[i].begin());
    for (int i=1; i<=n; i++)
        for (int j: adj[i])
            if (adj[j].size() >= 2)
            {
                bn[i]++;
                adj2[i].emplace_back(j);
                adj2[j].emplace_back(i);
                if (bn[i] > 2) return cout<<"impossible", 0;
            }
    for (int i=1; i<=n; i++) if (adj[i].size() >= 2) return cout<<(DFS(i) ? "possible" : "impossible"), 0;
    cout<<"possible";
}
/**
7 6
2 2
3 6
1 1
1 5
4 5
6 6
6 5
**/