#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

struct IdRegister {
    registered_ids: HashMap<(usize, usize), usize>,
    unused_id: usize,
}

impl IdRegister {
    fn new() -> IdRegister {
        IdRegister {
            registered_ids: HashMap::new(),
            unused_id: 0,
        }
    }

    fn query(&mut self, company: usize, station: usize) -> usize {
        if !self.registered_ids.contains_key(&(company, station)) {
            self.registered_ids
                .insert((company, station), self.unused_id);
            self.unused_id += 1;
        }
        self.registered_ids[&(company, station)]
    }
}

fn main() {
    let v: Vec<usize> = read_vec();
    let (n, m) = (v[0], v[1]);

    let mut lines = HashMap::new();
    let mut edges = Vec::new();
    let mut id_register = IdRegister::new();
    for _ in 0..m {
        let v: Vec<usize> = read_vec();
        let (s, t, c) = (v[0] - 1, v[1] - 1, v[2]);
        let s_edge_idx = id_register.query(c, s);
        let t_edge_idx = id_register.query(c, t);
        if edges.len() == s_edge_idx {
            edges.push(Vec::new());
        }
        if edges.len() == t_edge_idx {
            edges.push(Vec::new());
        }

        edges[s_edge_idx].push(Edge {
            to: t_edge_idx,
            cost: 0,
        });
        edges[t_edge_idx].push(Edge {
            to: s_edge_idx,
            cost: 0,
        });

        lines.entry(s).or_insert(HashSet::new()).insert(c);
        lines.entry(t).or_insert(HashSet::new()).insert(c);
    }

    // changable stations
    for station in lines.keys() {
        if lines[station].len() < 2 {
            continue;
        }
        let new_edges_idx = edges.len();
        edges.push(Vec::new());
        for &company in lines[station].iter() {
            edges[new_edges_idx].push(Edge {
                to: id_register.query(company, *station),
                cost: 1,
            });
            edges[id_register.query(company, *station)].push(Edge {
                to: new_edges_idx,
                cost: 1,
            });
        }
    }

    let new_edges_idx = edges.len();
    edges.push(Vec::new());
    if !lines.contains_key(&0) || !lines.contains_key(&(n - 1)) {
        println!("-1");
        return;
    }
    for &company in lines[&0].iter() {
        edges[new_edges_idx].push(Edge {
            to: id_register.query(company, 0),
            cost: 2,
        });
    }
    let d = dijkstra(&edges, new_edges_idx, new_edges_idx + 1);

    let mut ans = INF;
    for &company in lines[&(n - 1)].iter() {
        ans = min(ans, d[id_register.query(company, n - 1)]);
    }
    if ans == INF {
        println!("-1");
    } else {
        println!("{}", ans / 2);
    }
}

const INF: i32 = std::i32::MAX;

#[derive(PartialEq, Debug)]
struct MinInt {
    value: i32,
}

impl Eq for MinInt {}

impl PartialOrd for MinInt {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        other.value.partial_cmp(&self.value)
    }
}

impl Ord for MinInt {
    fn cmp(&self, other: &MinInt) -> Ordering {
        other.value.cmp(&self.value)
    }
}

fn make_pair(x: i32, y: usize) -> (MinInt, usize) {
    (MinInt { value: x }, y)
}

#[derive(Debug, Clone)]
struct Edge {
    to: usize,
    cost: i32,
}

fn dijkstra(edges: &Vec<Vec<Edge>>, start_idx: usize, num_apexes: usize) -> Vec<i32> {
    let mut d = vec![INF; num_apexes];
    d[start_idx] = 0;
    let mut que = BinaryHeap::new();
    que.push(make_pair(0, start_idx));

    while let Some((u, v)) = que.pop() {
        if d[v] < u.value {
            continue;
        }
        for e in &edges[v] {
            if d[e.to] > d[v] + e.cost {
                d[e.to] = d[v] + e.cost;
                que.push(make_pair(d[e.to], e.to));
            }
        }
    }
    d
}


Measured memory_bytes: 133372