#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{HashMap, HashSet, BinaryHeap, VecDeque, BTreeSet};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[allow(unused_imports)]
use std::io::stdin;

mod util {
    use std::io::stdin;
    use std::str::FromStr;
    use std::fmt::Debug;

    #[allow(dead_code)]
    pub fn line() -> String {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.trim().to_string()
    }

    #[allow(dead_code)]
    pub fn gets<T: FromStr>() -> Vec<T>
    where
        <T as FromStr>::Err: Debug,
    {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|t| t.parse().unwrap())
            .collect()
    }
}

#[allow(unused_macros)]
macro_rules! get {
    ($t:ty) => {
        {
            let mut line: String = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t:ty),*) => {
        {
            let mut line: String = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            (
                $(iter.next().unwrap().parse::<$t>().unwrap(),)*
            )
        }
    };
}

#[derive(Eq, PartialEq, Clone, Debug)]
struct Rev<T>(pub T);

impl<T: PartialOrd> PartialOrd for Rev<T> {
    fn partial_cmp(&self, other: &Rev<T>) -> Option<Ordering> {
        other.0.partial_cmp(&self.0)
    }
}

impl<T: Ord> Ord for Rev<T> {
    fn cmp(&self, other: &Rev<T>) -> Ordering {
        other.0.cmp(&self.0)
    }
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}


fn main() {
    let (n, m) = get!(usize, usize);
    let pqc: Vec<(usize, usize, usize)> = (0..m).map(|_| get!(usize, usize, usize)).collect();

    let mut edges = HashMap::new();
    let mut cs = vec![BTreeSet::new(); n];

    for &(p, q, c) in &pqc {
        let p = p - 1;
        let q = q - 1;
        edges.entry((p, c)).or_insert(BTreeSet::new()).insert(q);
        edges.entry((q, c)).or_insert(BTreeSet::new()).insert(p);

        cs[p].insert(c);
        cs[q].insert(c);
        /*
        edges.entry((p, Some(c))).or_insert(HashSet::new()).insert(
            (
                (p, None),
                0,
            ),
        );
        edges.entry((q, Some(c))).or_insert(HashSet::new()).insert(
            (
                (q, None),
                0,
            ),
        );
        */
        /*
        edges.entry((p, None)).or_insert(BTreeSet::new()).insert((
            (
                p,
                Some(c),
            ),
            1,
        ));
        edges.entry((q, None)).or_insert(BTreeSet::new()).insert((
            (
                q,
                Some(c),
            ),
            1,
        ));
        */
    }


    let mut que = BinaryHeap::new();
    let mut costs = HashMap::new();
    que.push(Rev((0, (0, None))));

    while !que.is_empty() {
        let Rev((cost, (station, company))) = que.pop().unwrap();

        if station == n - 1 {
            println!("{}", cost);
            return;
        }

        if let Some(c) = company {
            if let Some(e) = edges.get(&(station, c)) {
                for &to in e.iter() {
                    if costs.get(&(to, company)).cloned().unwrap_or(
                        u64::max_value(),
                    ) > cost
                    {
                        costs.insert((to, company), cost);
                        que.push(Rev((cost, (to, company))));
                    }
                }
            }
            let out = (station, None);
            if costs.get(&out).cloned().unwrap_or(u64::max_value()) > cost {
                costs.insert(out, cost);
                que.push(Rev((cost, out)));
            }
        } else {
            for &c in &cs[station] {
                let go = (station, Some(c));
                if costs.get(&go).cloned().unwrap_or(u64::max_value()) > cost + 1 {
                    costs.insert(go, cost + 1);
                    que.push(Rev((cost + 1, go)));
                }
            }
        }
    }


    println!("-1");
}


Measured memory_bytes: 139316