#include <bits/stdc++.h>

using namespace std;
#define FOR(i,n) for(int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;

template<typename ...> static inline int getchar_unlocked(void) { return getchar(); }
template<typename ...> static inline void putchar_unlocked(int c) { putchar(c); }
#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)
void reader(int& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
void reader(ll& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
int reader(char c[]) { int i, s = 0; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c[s++] = i; for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c[s++] = i; }c[s] = '\0'; return s; }
int reader(string& c) { int i; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c.push_back(i); for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c.push_back(i); }; return sz(c); }
template <class T, class S> void reader(T& x, S& y) { reader(x); reader(y); }
template <class T, class S, class U> void reader(T& x, S& y, U& z) { reader(x); reader(y); reader(z); }
template <class T, class S, class U, class V> void reader(T& x, S& y, U& z, V & w) { reader(x); reader(y); reader(z); reader(w); }
void writer(int x, char c) { int s = 0, m = 0; char f[10]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(ll x, char c) { int s = 0, m = 0; char f[20]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(const char c[]) { int i; for (i = 0; c[i] != '\0'; i++)mypc(c[i]); }
void writer(const char x[], char c) { int i; for (i = 0; x[i] != '\0'; i++)mypc(x[i]); mypc(c); }
template<class T> void writerLn(T x) { writer(x, '\n'); }
template<class T, class S> void writerLn(T x, S y) { writer(x, ' '); writer(y, '\n'); }
template<class T, class S, class U> void writerLn(T x, S y, U z) { writer(x, ' '); writer(y, ' '); writer(z, '\n'); }
template<class T> void writerArr(T x[], int n) { if (!n) { mypc('\n'); return; }FOR(i, n - 1)writer(x[i], ' '); writer(x[n - 1], '\n'); }
template<class T> void writerArr(vector<T>& x) { writerArr(x.data(), (int)x.size()); }

template<class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
ll mod_pow(ll a, ll n, ll mod) {
	ll ret = 1;
	ll p = a % mod;
	while (n) {
		if (n & 1) ret = ret * p % mod;
		p = p * p % mod;
		n >>= 1;
	}
	return ret;
}
template<class T> T extgcd(T a, T b, T& x, T& y) { for (T u = y = 1, v = x = 0; a;) { T q = b / a; swap(x -= q * u, u); swap(y -= q * v, v); swap(b -= q * a, a); } return b; }
template<class T> T mod_inv(T a, T m) { T x, y; extgcd(a, m, x, y); return (m + x % m) % m; }

using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

class UnionFind {
private:
	int n;
	vector<int> a;
public:
	UnionFind(int n) : n(n), a(n, -1) {}
	int find(int x) { return a[x] < 0 ? x : (a[x] = find(a[x])); }
	bool same(int x, int y) { return find(x) == find(y); }
	bool same(Pii& p) { return same(p.first, p.second); }
	bool unite(int x, int y) {
		x = find(x), y = find(y);
		if (x == y) return false;
		if (a[x] > a[y]) swap(x, y);
		a[x] += a[y];
		a[y] = x;
		n--;
		return true;
	}
	bool unite(Pii& p) { return unite(p.first, p.second); }
	int size() const { return n; }
	int size(int x) { return -a[find(x)]; }
};

vector<vector<int>> eg;
int solve(int n) {
	vector<int> cost(sz(eg), int(1e8));
	deque<int> q;
	q.push_back(0);
	cost[0] = 0;
	while (!q.empty()) {
		const int v = q.front(); q.pop_front();
		for (auto to : eg[v]) {
			int add = to >= n;
			int ncost = cost[v] + add;
			if (cost[to] > ncost) {
				cost[to] = ncost;
				if (add == 0) q.push_front(to);
				else q.push_back(to);
			}
		}
	}
	if (cost[n - 1] == ten(8)) cost[n - 1] = -1;
	return cost[n - 1];
}

int main() {
	int n, m; reader(n, m);
	unordered_map<int, vector<Pii>> mp;
	FOR(i, m) {
		int a, b, c; reader(a, b, c); a--; b--;
		mp[c].emplace_back(a, b);
	}
	
	int new_vertex = n;
	eg.reserve(2 * m);
	eg.resize(n);

	for (auto& kv : mp) {
		vector<int> cmp;
		for (auto& v : kv.second) {
			int a, b; tie(a, b) = v;
			cmp.emplace_back(a);
			cmp.emplace_back(b);
		}
		sort(cmp.begin(), cmp.end());
		cmp.erase(unique(cmp.begin(), cmp.end()), cmp.end());

		UnionFind uf(sz(cmp));
		for (auto& v : kv.second) {
			int a, b; tie(a, b) = v;
			a = lower_bound(cmp.begin(), cmp.end(), a) - cmp.begin();
			b = lower_bound(cmp.begin(), cmp.end(), b) - cmp.begin();
			uf.unite(a, b);
		}
		unordered_map<int, vector<int>> um;
		FOR(i, sz(cmp)) um[uf.find(i)].push_back(cmp[i]);
		for (auto& kv : um) {
			eg.emplace_back();
			for (auto& x : kv.second) {
				eg[x].push_back(new_vertex);
				eg[new_vertex].push_back(x);
			}
			new_vertex++;
		}
	}

	int ans = solve(n);
	writerLn(ans);

	return 0;
}

Measured memory_bytes: 35016