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

int n,m,a,b;
long long d;
bool conf[100010],confdfs[100010];
vector<pair<long long, int>> adj[100010];
set<pair<int, int>> prohib;
priority_queue<pair<long long,pair<int,int>>> pq;
vector<int> resp;

bool dfs(int pos){
    confdfs[pos]=true;
    resp.push_back(pos);
    if(pos==1) return true;
    for(int i=0;i<adj[pos].size();i++) if(!confdfs[adj[pos][i].second] && prohib.find({pos,adj[pos][i].second})==prohib.end()) if(dfs(adj[pos][i].second)) return true;
    resp.pop_back();
    return false;
}

int main(){
    scanf("%d %d", &n, &m);
    for(int i=0;i<m;i++){
        scanf("%d %d %lld", &a, &b, &d);
        adj[a].push_back({d,b});
        adj[b].push_back({d,a});
    }
    pq.push({0,{1,1}});
    while(!pq.empty()){
        int ant=pq.top().second.first;
        int prox=pq.top().second.second;
        d=pq.top().first;
        pq.pop();
        if(conf[prox]) continue;
        conf[prox]=true;
        prohib.insert({ant,prox});
        prohib.insert({prox,ant});
        for(int i=0;i<adj[prox].size();i++) pq.push({-d-adj[prox][i].first,{prox,adj[prox][i].second}});
    }
    if(dfs(0)){
        printf("%d", resp.size());
        for(int i=0;i<resp.size();i++) printf(" %d", resp[i]);
        printf("\n");
    }
    else printf("impossible\n");
    return 0;
}