#include <algorithm>
#include <bitset>
#include <cassert>
#include <complex>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeinfo>
#include <utility>
#include <vector>
#include <array>
#include <chrono>
#include <random>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;Scan(__VA_ARGS__);
template<typename T> void Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void Scan(First& first, Rest&...rest) { std::cin >> first; Scan(rest...); }
#define OUT(d) std::cout<<d;
#define FOUT(n, d) std::cout<<std::fixed<<std::setprecision(n)<<d;
#define SOUT(n, c, d) std::cout<<std::setw(n)<<std::setfill(c)<<d;
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define FLUSH std::cout<<std::flush;
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;
#define ALL(a) (a).begin(),(a).end()
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=(n)-1;i>=0;--i)
#define FORLL(i, a, b) for(ll i=ll(a);i<ll(b);++i)
#define RFORLL(i, a, b) for(ll i=ll(b)-1;i>=ll(a);--i)
#define REPLL(i, n) for(ll i=0;i<ll(n);++i)
#define RREPLL(i, n) for(ll i=ll(n)-1;i>=0;--i)
#define PAIR std::pair<int, int>
#define IN(a, x, b) (a<=x && x<b)
#define SHOW(d) {std::cout << #d << "\t:" << d << "\t";}
#define SHOWVECTOR(v) {std::cout << #v << "\t:";for(const auto& i : v){std::cout << i << " ";}std::cout << "\n";}
#define SHOWVECTOR2(v) {std::cout << #v << "\t:\n";for(const auto& i : v){for(const auto& j : i){std::cout << j << " ";}std::cout << "\n";}}
#define SHOWPAIRVECTOR2(v) {std::cout << #v << "\t:\n";for(const auto& i : v){for(const auto& j : i){std::cout<<'('<<j.first<<", "<<j.second<<") ";}std::cout << "\n";}}
#define SHOWPAIRVECTOR(v) {for(const auto& i:v){std::cout<<'('<<i.first<<", "<<i.second<<") ";}std::cout<<"\n";}
#define CHECKTIME(state) {auto start=std::chrono::system_clock::now();state();auto end=std::chrono::system_clock::now();auto res=std::chrono::duration_cast<std::chrono::nanoseconds>(end-start).count();std::cerr<<"[Time:"<<res<<"ns  ("<<res/(1.0e9)<<"s)]\n";}
#define SHOWQUEUE(a) {std::queue<decltype(a.front())> tmp(a);std::cout << #a << "\t:";for(int i=0; i<static_cast<int>(a.size()); ++i){std::cout << tmp.front() << "\n";tmp.pop();}std::cout << "\n";}

//#define int ll
using ll = long long;
using ull = unsigned long long;
constexpr int INFINT = 1 << 30;
constexpr ll INFLL = 1LL << 60;
constexpr double EPS = 0.0000000001;
constexpr int MOD = 1000000007;

//Union-Find
class UnionFind {
private:
	std::vector<int> parent;
	std::vector<int> height;

public:
	UnionFind() {}
	UnionFind(int size) : parent(size), height(size, 0) {
		REP(i, size) {
			parent[i] = i;
		}
	}
	void init(int size) {
		parent.resize(size);
		height.resize(size, 0);
		REP(i, size) {
			parent[i] = i;
		}
	}
	int find(int x) {
		if (parent[x] == x) {
			return x;
		}
		return parent[x] = find(parent[x]);
	}
	void unite(int x, int y) {
		x = find(x);
		y = find(y);
		if (x == y) return;
		if (height[x] < height[y]) parent[x] = y;
		else parent[y] = x;
		if (height[x] == height[y]) ++height[x];
	}
	bool same(int x, int y) {
		return find(x) == find(y);
	}
};

struct Node {
	std::set<ll> next;
	int dist;
	bool visited;
};

struct Company {
	UnionFind uf;
	std::unordered_set<int> node_list;
	std::unordered_map<int, int> node_map;
};

signed main() {
	INIT;
	VAR(int, n, m);
	std::vector<int> p(m), q(m), c(m);
	std::unordered_map<int, Company> com;

	// 入力 -------------------------------------------------------------------------------------------------------
	REP(i, m) {
		std::cin >> p[i] >> q[i] >> c[i];
		--p[i]; --q[i];
		com[c[i]].node_list.insert(p[i]);
		com[c[i]].node_list.insert(q[i]);
	}

	// 全体のノード番号 -> 会社のノード番号
	for (auto it_com = com.begin(); it_com != com.end(); ++it_com) {
		int num = 0;
		for (auto it_node = it_com->second.node_list.begin(); it_node != it_com->second.node_list.end(); ++it_node) {
			it_com->second.node_map[*it_node] = num++;
		}
		it_com->second.uf.init(num);
	}

	/*OUT("--------------------------------------")BR;
	for (auto it_com = com.begin(); it_com != com.end(); ++it_com) {
		SHOW(it_com->first)BR;
		for (auto it_node = it_com->second.node_list.begin(); it_node != it_com->second.node_list.end(); ++it_node) {
			OUT(*it_node)TAB;
		}BR;
		for (auto it_node = it_com->second.node_map.begin(); it_node != it_com->second.node_map.end(); ++it_node) {
			OUT(it_node->second)TAB;
		}BR;
	}FLUSH;
	OUT("--------------------------------------")BR;*/

	// 頂点同士を繋げる --------------------------------------------------------------------------------------------
	REP(i, m) {
		com[c[i]].uf.unite(com[c[i]].node_map[p[i]], com[c[i]].node_map[q[i]]);
	}

	// (会社番号, 路線番号(UFの親)) -> ノード番号 と対応付ける関数 -----------------------------------------------------
	auto route_to_num = [&](const int& c, const int& r) -> ll {
		return (ll)c * 100000 + r;
	};

	// グラフ(キー番号が非連続のためhash map)
	std::unordered_map<ll, Node> node;

	// グラフの隣接リストに頂点間の繋がりを格納する -------------------------------------------------------------------
	REP(i, m) {
		int par = com[c[i]].uf.find(com[c[i]].node_map[p[i]]);
		node[p[i]].next.insert(route_to_num(c[i], par));
		node[q[i]].next.insert(route_to_num(c[i], par));
		node[route_to_num(c[i], par)].next.insert(p[i]);
		node[route_to_num(c[i], par)].next.insert(q[i]);
	}

	// BFS -------------------------------------------------------------------------------------------------------
	std::queue<ll> queue;
	node[0].dist = 1;
	node[0].visited = true;
	queue.push(0);
	while (!queue.empty()) {
		const ll now_i = queue.front(); queue.pop();
		const Node& now = node[now_i];
		for (const auto& check_i : now.next) {
			Node& check = node[check_i];
			if (!check.visited) {
				check.dist = now.dist + 1;
				check.visited = true;
				queue.push(check_i);
			}
		}
	}
	/*OUT("--------------------------------------")BR;
	SHOW(node.size())BR;
	for (auto it = node.begin(); it != node.end(); ++it) {
		SOUT(13, '_', it->first + 1)BR;
		for (auto now : it->second.next) {
			SOUT(20, ' ', now + 1)BR;
		}
	}
	OUT("--------------------------------------")BR;*/

	int ans = node[n - 1].dist / 2;
	if (ans == 0) --ans;
	OUT(ans)BR;
	return 0;
}

Measured memory_bytes: 157684