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

#define st first
#define nd second
#define pb push_back
#define int long long

typedef pair<int,int> pii;
typedef pair<int,pii> piii;

const int N = 1e5+5 , inf = 1e14;

int n , m , disti[N] , distf[N] , vis[N] , p[N];
vector<pii> adj[N];
bool ok;
vector<int> vec;

void Djikstra(int u , int *dist){
  priority_queue<pii , vector<pii> , greater<pii> > fila;
  for(int i = 0 ; i < n ; i++) dist[i] = inf;
  fila.push({0,u}) , dist[u] = 0;
  while(!fila.empty()){
    u = fila.top().nd , fila.pop();
    for(auto v : adj[u])
      if(dist[v.st] > dist[u] + v.nd)
        dist[v.st] =  dist[u] + v.nd , fila.push({dist[v.st],v.st});
  }
}

void dfs(int u){
  vis[u] = 1;
  if(u == 1 || ok){ok = true; return;}
  for(auto v : adj[u])
    if(distf[v.st] + v.nd > distf[u]  && vis[v.st] == 0) dfs(v.st) , p[v.st] = u;
}

main(){

  ios_base::sync_with_stdio(0),cin.tie(0);

  cin >> n >> m;

  memset(p,-1,sizeof(-1));
  for(int i = 0 ; i < m ; i++){
    int x , y , z;
    cin >> x >> y >> z;
    adj[x].pb({y,z}) , adj[y].pb({x,z});
  }

  Djikstra(0,disti) , Djikstra(1,distf) , ok = false , dfs(0);

  if(vis[1] == 0) cout << "impossible\n";

  else{
    int u = 1;
    while(u != 0){vec.pb(u) , u = p[u];}
    vec.pb(0);
    cout << vec.size() << " ";
    for(int i = vec.size() - 1 ; i >= 0 ; i--) cout << vec[i] << " ";
    cout << "\n";
  }

}