#include <bits/stdc++.h>
 
#define _overload(_1,_2,_3,name,...) name
#define _rep(i,n) _range(i,0,n)
#define _range(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload(__VA_ARGS__,_range,_rep,)(__VA_ARGS__)
 
#define _rrep(i,n) _rrange(i,n,0)
#define _rrange(i,a,b) for(int i=(int)(a)-1;i>=(int)(b);--i)
#define rrep(...) _overload(__VA_ARGS__,_rrange,_rrep,)(__VA_ARGS__)
 
#define _all(arg) begin(arg),end(arg)
#define uniq(arg) sort(_all(arg)),(arg).erase(unique(_all(arg)),end(arg))
#define getidx(ary,key) lower_bound(_all(ary),key)-begin(ary)
#define clr(a,b) memset((a),(b),sizeof(a))
#define bit(n) (1LL<<(n))
 
// #define DEBUG
 
#ifdef DEBUG
    #define dump(...) fprintf(stderr, __VA_ARGS__)
#else
    #define dump(...)
#endif
 
template<class T>bool chmax(T &a, const T &b) { return (a<b)?(a=b,1):0;}
template<class T>bool chmin(T &a, const T &b) { return (b<a)?(a=b,1):0;}
 
using namespace std;
using ll=long long;
using vi=vector<int>;
using vll=vector<ll>;
 
const double EPS = 1e-10;
const double PI = acos(-1.0);
const int inf =INT_MAX;
const ll mod=1000000007LL;
const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};
 
 
ll extgcd(ll a,ll b,ll& x,ll& y){x=1,y=0;ll g=a;if(b!=0) g=extgcd(b,a%b,y,x),y-=a/b*x;return g;}
ll ADD(const ll &a, const ll &b,const ll &mod) { return (a+b)%mod;}
ll SUB(const ll &a, const ll &b,const ll &mod) { return (a-b+mod)%mod;}
ll MUL(const ll &a, const ll &b,const ll &mod) { return (1LL*a*b)%mod;}
ll DIV(const ll &a, const ll &b,const ll &mod) {ll x,y; extgcd(b,mod,x,y);return MUL(a,(x+mod)%mod,mod);}
 
random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1,6);
uniform_real_distribution<double> score(0.0,10.0);

#include <sys/time.h>
double gett(){
  struct timeval t;
  gettimeofday(&t,NULL);
  return t.tv_sec + t.tv_usec/1e6;
}

int main(void){
    double st = gett();

    cin.tie(0);
    ios::sync_with_stdio(false);

    int n, m; cin >> n >> m;
    using Edge = tuple<int, int>;
    vector<vector<Edge>> G(n);
    rep(loop, m){
        int a, b, c; cin >> a >> b >> c;
        a--, b--;
        G[a].emplace_back(Edge(c, b));
        G[b].emplace_back(Edge(c, a));
    }
    rep(i, n) sort(_all(G[i]));

    using Elem = tuple<int, int, int>;
    priority_queue<Elem, vector<Elem>, greater<Elem>> q;
    int sz = 0;
    vector<unordered_map<int, int>> p2i(n);
    rep(i, n){
        set<int> s = {0};
        for(auto& e : G[i]){
            s.insert(get<0>(e));
        }
        for(auto& e : s){
            p2i[i][e] = sz++;
        }
    }
    vi min_dist(sz, inf);
    q.push(Elem(0, 0, 0));
    min_dist[0] = 0;

    int res = -1;
    while(q.size()){
        int cost, v, pc; tie(cost, v, pc) = q.top(); q.pop();
        if(cost != min_dist[p2i[v][pc]]) continue;

        if(v == n - 1){
            res = cost;
            break;
        }

        if(pc == 0){
            for(auto& e : G[v]){
                int nv, nc; tie(nc, nv) = e;
                int ncost = cost + 1;
                int idx = p2i[nv][nc];
                if(chmin(min_dist[idx], ncost)){
                    min_dist[idx] = ncost;
                    q.push(Elem(ncost, nv, nc));
                }
            }
        }
        else {
            auto itr = lower_bound(_all(G[v]), Edge(pc, 0));
            while(itr != end(G[v]) and get<0>(*itr) == pc){
                int nv = get<1>(*itr);
                int nc = pc;
                int ncost = cost;
                int idx = p2i[nv][nc];
                if(chmin(min_dist[idx], ncost)){
                    min_dist[idx] = ncost;
                    q.push(Elem(ncost, nv, nc));
                }
                itr++;
            }
        }

        if(pc != 0){
            int idx = p2i[v][0];
            if(chmin(min_dist[idx], cost)){
                min_dist[idx] = cost;
                q.push(Elem(cost, v, 0));
            }
        }
    }

    cout << res << endl;

    return 0;
}


Measured memory_bytes: 43376