#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=INF;
const ll MAX=1000010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;





signed main(){
    ll n,m;cin>>n>>m;
    vector<vector<pair<ll,pair<ll,char> > > >G(n);
    ll u=-1,v=-1;
    char cc='.';
    ll ccc=0;
    rep(i,m){
        ll a,b;char c;
        cin>>a>>b>>c;a--,b--;
        G[a].pb(mp(b,mp(i+1,c)));
        G[b].pb(mp(a,mp(i+1,c)));
    }

    rep(i,n){
        for(auto e:G[i]){
            if(e.se.se!=G[0][0].se.se){
                u=i,v=e.fi;cc=e.se.se;
                ccc=e.se.fi;
            }
        }
    }

    if(u==-1){
        cout<<v<<endl;
        return 0;
    }

    vector<ll>d(n,inf);
    d[0]=0;
    queue<ll>q;
    vector<ll>p(0);
    q.push(0);
    while(!q.empty()){
        ll k=q.front();
        q.pop();
        for(auto e:G[k]){
            if(d[e.fi]<inf){
                continue;
            }
            d[e.fi]=d[k]+1;
            q.push(e.fi);
        }
    }
    string pre="";
    while(d[u]>0){
        ll nxt=-1;
        char c='.';
        for(auto e:G[u]){
            if(d[e.fi]==d[u]-1){
                nxt=e.fi;
                c=e.se.se;
                p.pb(e.se.fi);
                break;
            }
        }
        pre+=c;
        u=nxt;
    }

    vector<ll>dd(n,inf);
    dd[n-1]=0;
    q.push(n-1);
    while(!q.empty()){
        ll k=q.front();
        q.pop();
        for(auto e:G[k]){
            if(dd[e.fi]<inf){
                continue;
            }
            dd[e.fi]=dd[k]+1;
            q.push(e.fi);
        }
    }
    reverse(all(p));
    reverse(all(pre));
    p.pb(ccc);
    string sur="";
    while(dd[v]>0){

        ll nxt=-1;
        char c='.';
        for(auto e:G[v]){
            if(dd[e.fi]==dd[v]-1){
                nxt=e.fi;
                c=e.se.se;
                p.pb(e.se.fi);
                break;
            }
        }
        sur+=c;
        v=nxt;
    }
    string ans=pre+cc+sur;
    string ans2=ans;
    reverse(all(ans));
    reverse(all(p));
    if(ans2==ans){
        p.pb(G[0][0].se.fi);
        p.pb(G[0][0].se.fi);
    }
    reverse(all(p));
    cout<<p.size()<<endl;
    rep(i,p.size()){
        cout<<p[i]<<endl;
    }
}