// see https://github.com/LumaKernel/vimfiles/tree/master/snippets/cp-cpp/temp.snip
/// --- .lumrc Template {{{ ///
// #define DEBUG
// #define assert(...)
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = tuple<int, int>;
using P3 = tuple<int, int, int>;
using VI = vector<int>;
using VL = vector<ll>;
using VVI = vector<VI>;
using VVL = vector<VL>;
using VP = vector<P>;
using VP3 = vector<P3>;
using VS = vector<string>;

#define omajinai ios::sync_with_stdio(false),cin.tie(0)

#define FOR(i,a,b) for(int i=int(a);i<int(b);++i)
#define FORI(i,a,b) for(int i=int(a);i<=int(b);++i)
#define REP(i,n) FOR(i,0,n)
#define REPI(i,n) FORI(i,0,n)
#define RFOR(i,a,b) for(int i=int(b)-1;i>=int(a);--i)
#define RFORI(i,a,b) for(int i=int(b);i>=int(a);--i)
#define RREP(i,n) RFOR(i,0,n)
#define RREPI(i,n) RFORI(i,0,n)

#define ALL(a) begin(a),end(a)
#define UNIQUE(a) (a).erase(unique(ALL(a)),(a).end())
#define PB push_back
#define EACH(i,c) REP(i,(c).size())
#define REACH(i,c) RREP(i,(c).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort(ALL(c))

#define BR cout<<"\n";

#ifdef DEBUG
#define dump(...) cerr<<"["<<__LINE__<< "] "<<#__VA_ARGS__<<" = "<<make_tuple(__VA_ARGS__)<<"\n";
#else
#define dump(...)
#endif

#define YES(x) cout<<((x)?"YES":"NO")<<"\n";
#define Yes(x) cout<<((x)?"Yes":"No")<<"\n";
#define yes(x) cout<<((x)?"yes":"no")<<"\n";

int __int_temp; ll __ll_temp; string __string_temp;
#define oini (omajinai, cin>>__int_temp, __int_temp)
#define oinl (omajinai, cin>>__ll_temp, __ll_temp)
#define oins (omajinai, cin>>__string_temp, __string_temp)
#define ini (cin>>__int_temp, __int_temp)
#define inl (cin>>__ll_temp, __ll_temp)
#define ins (cin>>__string_temp, __string_temp)

#define isInside(y,x) (0<=(y)&&(y)<h&&0<=(x)&&(x)<w)

#define fi(x) (get<0>(x))
#define se(x) (get<1>(x))
#define th(x) (get<2>(x))
#define fo(x) (get<3>(x))
#define fif(x) (get<4>(x))

template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) { o << '{'; EACH(i, v) o << v[i] << (i != (int)v.size()-1 ? ", " : ""); o << "}";  return o; }

template<int n, class...T> typename enable_if<(n>=sizeof...(T))>::type _ot(ostream &, tuple<T...> const &){}
template<int n, class...T> typename enable_if<(n< sizeof...(T))>::type _ot(ostream & os, tuple<T...> const & t){ os << (n==0?"":", ") << get<n>(t); _ot<n+1>(os, t); }
template<class...T> ostream & operator<<(ostream & os, tuple<T...> const & t){ _ot<0>(os, t); return os; }

template <typename T> inline void smax(T &a, T b) { a = a > b ? a : b; }
template <typename T> inline void smin(T &a, T b) { a = a < b ? a : b; }

template<typename T> inline int intlog2(T x);
template<> inline int intlog2(int x) { return x == 0 ? 0 : 32 - __builtin_clz(x); }
template<> inline int intlog2(ll x) { return x == 0 ? 0 : 64 - __builtin_clzll(x); }

constexpr double PI = acos(-1);

/// }}}--- ///

constexpr int INF = 1e9+1;
constexpr ll LINF = 1e18+1;
constexpr int MOD = 1e9+7;

const int N = 1e5 + 100;
VI cols[N];
map<int, VI> g[N];
map<int, int> dist[N];
int main() {
  omajinai;
  int n=ini,m=ini;
  REP(i,m) {
    int p,q,r;
    cin>>p>>q>>r;
    p--;q--;
    cols[p].PB(r);
    cols[q].PB(r);
    g[p][r].PB(q);
    g[q][r].PB(p);
  }
  deque<P3> deq;
  deq.emplace_back(0, 0, -1);
  dist[0][-1] = 0;
  while(deq.size()) {
    auto dat = deq.front(); deq.pop_front();
    int d = fi(dat), i = se(dat), k = th(dat);
    if(i == n-1) {
      cout << d << endl;
      return 0;
    }
    if(k == -1) {
      for(int c : cols[i]) if(!dist[i].count(c) || d+1 < dist[i][c]) {
        dist[i][c] = d + 1;
        deq.emplace_back(d + 1, i, c);
      }
    } else {
      for(int j : g[i][k]) if(!dist[j].count(k) || d < dist[j][k]) {
        dist[j][k] = d;
        deq.emplace_front(d, j, k);
      }
      if(!dist[i].count(-1) || d < dist[i][-1]) {
        dist[i][-1] = d;
        deq.emplace_front(d, i, -1);
      }
    }
  }
  cout << -1 << endl;
}


Measured memory_bytes: 76928