use std::collections::{HashSet, VecDeque};

fn main() {
    let (n, m) = input_tuple();
    let u_v = input_tuple_vec::<usize>(m);

    let mut list = vec![Vec::new(); n];

    for &(u, v) in &u_v {
        list[u - 1].push(v - 1);
    }

    let start = (0, false, false);

    // ----------------------------------

    // let mut visited = vec![false; n];
    let mut visited = HashSet::new();

    let mut queue = VecDeque::new();
    queue.push_back((start, 0));
    visited.insert(start);

    // let mut steps = vec![usize::MAX; n];
    // steps[start] = 0;

    while let Some(((current, visit_n, visit_n_1), step)) = queue.pop_front() {
        if current == 0 && visit_n && visit_n_1 {
            println!("{}", step);
            return;
        }

        let mut next_visit_n = visit_n;
        let mut next_visit_n_1 = visit_n_1;

        if current == n - 1 {
            next_visit_n = true;
        }

        if current == n - 2 {
            next_visit_n_1 = true;
        }

        for &next in list[current].iter() {
            if visited.contains(&(next, next_visit_n, next_visit_n_1)) {
                continue;
            }

            // 次へ
            visited.insert((next, next_visit_n, next_visit_n_1));
            queue.push_back(((next, next_visit_n, next_visit_n_1), step + 1));
        }
    }

    println!("-1");
}

fn input_tuple<T>() -> (T, T)
where
    T: std::str::FromStr,
    <T as std::str::FromStr>::Err: std::fmt::Debug,
{
    let stdin = std::io::stdin();

    let mut buf = String::new();
    stdin.read_line(&mut buf).unwrap();
    buf = buf.trim_end().to_owned();

    let mut iter = buf.split_whitespace();

    let n = iter.next().unwrap().parse().unwrap();
    let m = iter.next().unwrap().parse().unwrap();

    (n, m)
}

fn input_tuple_vec<T>(n: usize) -> Vec<(T, T)>
where
    T: std::str::FromStr,
    <T as std::str::FromStr>::Err: std::fmt::Debug,
{
    // タプルのベクタ

    let stdin = std::io::stdin();

    let mut s_t_d = Vec::with_capacity(n);

    for _ in 0..n {
        let mut buf = String::new();
        stdin.read_line(&mut buf).unwrap();
        buf = buf.trim_end().to_owned();

        let mut iter = buf.split_whitespace();

        let s = iter.next().unwrap().parse().unwrap();
        let t = iter.next().unwrap().parse().unwrap();
        // let d = iter.next().unwrap().parse().unwrap();

        s_t_d.push((s, t));
    }

    s_t_d
}