#include <bits/stdc++.h>

using namespace std;

#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()
#define endl "\n"
#define rep(i, a, b) for (auto (i) = (a); (i) < (b); (i)++)
#define rrep(i, a, b) for (auto (i) = (a); (i) > (b); (i)--)

#define aim_cpo do{ios::sync_with_stdio(false);\
cin.tie(nullptr);cout.precision(12);cout<<fixed;}while(0)

#define LOCAL_INPUT do{FILE *stream1;\
stream1=freopen("/Users/aim_cpo/CLionProjects/competitive/in.txt","r",stdin);\
if(stream1==nullptr)return 0;}while(0)
#define LOCAL_OUTPUT do{FILE *stream2;\
stream2 = freopen("out.txt", "w", stdout);\
if (stream2 == nullptr) return 0;}while(0)

#ifdef LOCAL_DEFINE
#define show(x) cerr << #x << " = " << (x) << endl
#define showV(v, n) do{\
for(int _i_t_e_=0; _i_t_e_<(n);_i_t_e_++)\
cerr<<"("<<_i_t_e_<<" = "<<(v)[_i_t_e_]<<") ";\
cerr<<endl;}while(0)
#define showA(a, n) do{\
for(int _i_t_e_=0;_i_t_e_<(n);_i_t_e_++)\
cerr<<"("<<_i_t_e_<<" = "<<(a)[_i_t_e_]<<") ";\
cerr<<endl;}while(0)
#define showA2(a, n, m) do{\
for(int _i_t_e_=0;_i_t_e_<(n);_i_t_e_++){\
for(int _i_t_e_2=0;_i_t_e_2<(m);_i_t_e_2++){\
cerr<<"("<<_i_t_e_<<", "<<_i_t_e_2<<" = "<<(a)[_i_t_e_][_i_t_e_2]<<") ";\
}cerr<<endl;}cerr<<endl;}while(0)
#else
#define show(x)
#define showV(v, n)
#define showA(a, n)
#define showA2(a, n, m)
#endif

typedef long long ll;
typedef unsigned long long ull;

constexpr const int INT_INF=0x3f3f3f3f; //1061109567
constexpr const ll LL_INF=0x3f3f3f3f3f3f3f3f; //4557430888798830399

template <typename T> bool chmin(T &a, T b){return a>b?(a=b,true):false;}
template <typename T> bool chmax(T &a, T b){return a<b?(a=b,true):false;}
template <typename T> void ln(T i, T n){cout<<(i==n-1?"\n":" ");}
template <typename T, typename S>
ostream &operator<<(ostream &out,const pair<T, S> &pair1){
  out<<'('<<pair1.fi<<", "<<pair1.se<<')';return out;}

// INT
#define GCD(a, b) __gcd(a, b)
template <typename T> T LCM(T a, T b) {return a / GCD(a, b) * b;}
template <typename T> T EXTGCD(T a, T b, T& x, T& y) {
  T d = a;
  if (b != 0) {d=EXTGCD(b,a%b,y,x);y-=(a/b)*x;}
  else x=1,y=0;
  return d;
}
template <typename T> bool is_prime(T a) {
  for(int i=2;i*i<=a;i++)if(a%i==0)return 1;
  return 0;
}

// MOD
ll MOD = 1000000000L + 7L;
#define add(a, b) ((a % MOD) + (b % MOD)) % MOD
#define mul(a, b) ((a % MOD) * (b % MOD)) % MOD
#define sub(a, b) ((a % MOD) + MOD - (b % MOD)) % MOD
template <typename T> T mod_inverse(T a, T mod, bool prime){ // if mod is prime, "prime" is true.
  if(prime){
    T tmp=mod-2,now=a,res=1;while(tmp){if(tmp&1)res=mul(res,now);now=mul(now,now);tmp>>=1;}
    return res;
  }else{T x,y;EXTGCD(a,mod,x,y);return (mod+x%mod)%mod;}
}
#define divide(a, b) ((a % MOD) * (mod_inverse(b, MOD, true))) % MOD

//LLの数値をつかう時は最後にLをつける癖をつけよう
//
//  ┏┓┏┓　┓　┏┓
//  ┏┛┃┃　┃　┗┫
//  ┗┛┗┛　┻　┗┛
//
//   謹┃賀┃新┃年┃
//   ━┛━┛━┛━┛
//WWWWWWWWWWWWWWWWWWWWWW

int n, m;
vector <pair <int, int> > v[512345];
ll d[512345];

int EdgeNum = 100000;
map <pair<int, int> , int> map1;
map <int, pair<int, int> > map2;

void AddEdge(int a, int b, int c) {
  if (map1.find(mp(a, c)) == map1.end()) {
    map2[EdgeNum] = mp(a, c);
    map1[mp(a, c)] = EdgeNum++;
  }
  if (map1.find(mp(b, c)) == map1.end()) {
    map2[EdgeNum] = mp(b, c);
    map1[mp(b, c)] = EdgeNum++;
  }
  v[map1[mp(a, c)]].emplace_back(a, 1);
  v[a].emplace_back(map1[mp(a, c)], 1);
  v[map1[mp(a, c)]].emplace_back(map1[mp(b, c)], 0);
  v[map1[mp(b, c)]].emplace_back(map1[mp(a, c)], 0);
  v[map1[mp(b, c)]].emplace_back(b, 1);
  v[b].emplace_back(map1[mp(b, c)], 1);
}

int main() {
  aim_cpo; // インタラクティブのときは消すように.
#ifdef LOCAL_DEFINE
  LOCAL_INPUT; // インタラクティブのときは消すように.
//  LOCAL_OUTPUT; // ファイルに出力したいときのみ
  show(MOD);
#endif
  cin >> n >> m;
  rep(i, 0, m) {
    int from, to, c; cin >> from >> to >> c;
    from--; to--; c--;
    AddEdge(from, to, c);
  }
  fill(d, d + 512345, LL_INF);
  priority_queue<pair<ll, int> > q;
  q.push(mp(0, 0));
  d[0] = 0;
  while (!q.empty()) {
    int now = q.top().se; ll cost = -q.top().fi; q.pop();
    if (now < n) show(now);
    else show(map2[now]);
    show(cost);
    if (d[now] < cost) continue;
    rep(i, 0, (int)v[now].size()) {
      int next = v[now][i].fi;
      ll nextcost = cost + v[now][i].se;
      if (d[next] > nextcost) {
        d[next] = nextcost;
        q.push(mp(-nextcost, next));
      }
    }
  }
  if (d[n - 1] == LL_INF) cout << -1 << endl;
  else {
    assert(d[n - 1] % 2 == 0);
    cout << d[n - 1] / 2 << endl;
  }
#ifdef  LOCAL_DEFINE
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "s." << endl;
#endif
  return 0;
}

Measured memory_bytes: 86516