#include<bits/stdc++.h>
using namespace std;
signed main(){
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int N,M; cin >> N >> M;
  vector<vector<int>> graph(N);
  vector<int> D(N, 0), parent(N, 0);
  for(int i = 0; i < M; i++){
    int u,v; cin >> u >> v;
    graph[u - 1].emplace_back(v - 1);
  }
  queue<int> q;
  q.push(0);
  D[0] = 1;
  parent[0] = -1;
  while(!q.empty()){
    int node = q.front();
    q.pop();
    for(int v : graph[node]){
      if(D[v] < D[node] + 1){
        D[v] = D[node] + 1;
        parent[v] = node;
        q.push(v);
      }
    }
  }
  if(D[N - 1] == 0){
    cout << "IMPOSSIBLE\n";
    return 0;
  }
  cout << D[N - 1] << '\n';
  vector<int> answer;
  int node = N - 1;
  while(node != -1){
    answer.emplace_back(node + 1);
    node = parent[node];
  }
  reverse(answer.begin(), answer.end());
  for(int e : answer)
    cout << e << ' ';
}