#![allow(unused_imports)]
#![allow(dead_code)]
#![allow(unused_variables)]
#![warn(non_snake_case)]

//use itertools::Itertools;
use std::cmp::{max, min, Reverse};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
use std::f64::consts::PI;
use std::io::prelude::*;
use std::io::{stdin, stdout, BufWriter, Write};
use std::time::Instant;

/*
use rand::distributions::{Distribution, Uniform};
use rand_chacha::{rand_core::SeedableRng, ChaCha8Rng};
use core::ops::{Add,Sub,Mul,Div};
use itertools::Itertools;
*/

const M1: i64 = 1000_000_007;
const M2: i64 = 998244353;
fn main() {
    //let mut out: BufWriter<std::io::StdoutLock<'_>> = BufWriter::new(stdout().lock());

    input! {
        n: usize,
        m: usize,
        uv: [(usize,usize);m]
    }

    let mut edge = vec![];
    for i in 0..m {
        edge.push((uv[i].0, uv[i].1, 1));
    }

    let mut ans1: i64 = 0;

    let mut ans2: i64 = 0;

    let (dist1, set) = Dijkstra(1, n, m, &edge);

    let (distn1, set) = Dijkstra(n - 1, n, m, &edge);

    let (distn, set) = Dijkstra(n, n, m, &edge);

    if dist1[n - 1] == usize::MAX {
        ans1 += 1000_000_000_000;
    } else {
        ans1 += dist1[n - 1] as i64;
    }

    if distn1[n] == usize::MAX {
        ans1 += 1000_000_000_000;
    } else {
        ans1 += distn1[n] as i64;
    }

    if distn[1] == usize::MAX {
        ans1 += 1000_000_000_000;
    } else {
        ans1 += distn[1] as i64;
    }

    if dist1[n] == usize::MAX {
        ans2 += 1000_000_000_000;
    } else {
        ans2 += dist1[n] as i64;
    }

    if distn[n - 1] == usize::MAX {
        ans2 += 1000_000_000_000;
    } else {
        ans2 += distn[n - 1] as i64;
    }

    if distn1[1] == usize::MAX {
        ans2 += 1000_000_000_000;
    } else {
        ans2 += distn1[1] as i64;
    }

    if ans1 > 1000_000_000_000 && ans2 > 1000_000_000_000 {
        println!("{}", -1);
    } else {
        println!("{}", min(ans1, ans2));
    }

    //write!(out,"{}\n",ans).unwrap();
}

// Dijkstra法
// 指定した頂点からその他全ての頂点間の最小コストを求めるアルゴリズム
// ただし辺のコストは必ず正
// xから1からnまでの頂点への最小コストを持つVectorを返す
// x: 出発点
// n: 頂点数
// m: 辺の数
// edge: Vec<(頂点a、頂点b、コスト)>
// distとset(最短経路とスパニングツリーの辺)を返す
// 計算量O(NlogN)
pub fn Dijkstra(
    x: usize,
    n: usize,
    m: usize,
    edge: &Vec<(usize, usize, usize)>,
) -> (Vec<usize>, HashSet<i32>) {
    let mut g = vec![vec![]; n + 1];
    for i in 0..m {
        g[edge[i].0].push((edge[i].1, edge[i].2, i as i32 + 1));
    }

    let mut set = HashSet::new();
    // dist[i]: xからiまでの最小コスト
    let mut dist = vec![usize::MAX; n + 1];
    // confirm[i]: iが巡回済みであるがどうか
    let mut confirm = vec![false; n + 1];
    dist[x] = 0;
    // 最短経路の候補
    let mut heap = BinaryHeap::new();
    heap.push((Reverse(0), x, -1));
    while !heap.is_empty() {
        // 頂点vのコストは_dで確定の可能性
        let (Reverse(_d), v, edge_i) = heap.pop().unwrap();
        // すでに頂点vのコストが確定している場合は飛ばす
        if confirm[v] {
            continue;
        }
        //vのコストが確定
        confirm[v] = true;
        if edge_i != -1 {
            set.insert(edge_i);
        }
        //vの隣接ノードに関して最短距離確定の候補をpush
        for &(i, cost, edge_i) in &g[v] {
            if dist[i] > dist[v] + cost {
                dist[i] = dist[v] + cost;
                heap.push((Reverse(dist[i]), i, edge_i));
            }
        }
    }
    return (dist, set);
}

pub mod my_proconio {
    #[macro_export]
    macro_rules! input {
        (source = $s:expr, $($r:tt)*) => {
            let mut iter = $s.split_whitespace();
            let mut next = || { iter.next().unwrap() };
            input_inner!{next, $($r)*}
        };
        ($($r:tt)*) => {
            let stdin = std::io::stdin();
            let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
            let mut next = move || -> String{
                bytes
                    .by_ref()
                    .map(|r|r.unwrap() as char)
                    .skip_while(|c|c.is_whitespace())
                    .take_while(|c|!c.is_whitespace())
                    .collect()
            };
            input_inner!{next, $($r)*}
        };
    }

    #[macro_export]
    macro_rules! input_inner {
        ($next:expr) => {};
        ($next:expr, ) => {};

        ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
            let $var = read_value!($next, $t);
            input_inner!{$next $($r)*}
        };

        ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
            let mut $var = read_value!($next, $t);
            input_inner!{$next $($r)*}
        };
    }

    #[macro_export]
    macro_rules! read_value {
        ($next:expr, ( $($t:tt),* )) => {
            ( $(read_value!($next, $t)),* )
        };

        ($next:expr, [ $t:tt ; $len:expr ]) => {
            (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
        };

        ($next:expr, chars) => {
            read_value!($next, String).chars().collect::<Vec<char>>()
        };

        ($next:expr, usize1) => {
            read_value!($next, usize) - 1
        };

        ($next:expr, $t:ty) => {
            $next().parse::<$t>().expect("Parse error")
        };
    }
}