#![allow(non_snake_case, unused_imports, unused_must_use)]
use std::io::{self, prelude::*};
use std::str;

fn main() {
    let (stdin, stdout) = (io::stdin(), io::stdout());
    let mut scan = Scanner::new(stdin.lock());
    let mut out = io::BufWriter::new(stdout.lock());

    macro_rules! input {
        ($T: ty) => {
            scan.token::<$T>()
        };
        ($T: ty, $N: expr) => {
            (0..$N).map(|_| scan.token::<$T>()).collect::<Vec<_>>()
        };
    }

    let N = input!(usize);
    let M = input!(usize);

    let mut graph = vec![vec![]; N];

    for _ in 0..M {
        let (u, v) = (input!(usize) - 1, input!(usize) - 1);
        graph[u].push(v);
    }

    let bfs = |start: usize| {
        let mut dist = vec![1_usize << 30; N];
        let mut seen = vec![false; N];
        let mut q = std::collections::VecDeque::new();

        dist[start] = 0;
        seen[start] = true;
        q.push_front(start);

        while let Some(now) = q.pop_front() {
            for &nxt in graph[now].iter() {
                if seen[nxt] {
                    continue;
                }

                dist[nxt] = dist[now] + 1;
                seen[nxt] = true;
                q.push_back(nxt);
            }
        }

        return dist;
    };

    let dist_from0 = bfs(0);
    let dist_fromNm1 = bfs(N - 2);
    let dist_fromN = bfs(N - 1);

    let mut ans = 1_usize << 30;
    // 1 -> N - 1 -> N -> 1
    let ans1 = dist_from0[N - 2] + dist_fromNm1[N - 1] + dist_fromN[0];
    // 1 -> N -> N - 1 -> 1
    let ans2 = dist_from0[N - 1] + dist_fromN[N - 2] + dist_fromNm1[0];

    ans = std::cmp::min(ans, ans1);
    ans = std::cmp::min(ans, ans2);

    if ans == 1 << 30 {
        writeln!(out, "-1");
    } else {
        writeln!(out, "{}", ans);
    }
}

struct Scanner<R> {
    reader: R,
    buf_str: Vec<u8>,
    buf_iter: str::SplitWhitespace<'static>,
}
impl<R: BufRead> Scanner<R> {
    fn new(reader: R) -> Self {
        Self {
            reader,
            buf_str: vec![],
            buf_iter: "".split_whitespace(),
        }
    }
    fn token<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buf_iter.next() {
                return token.parse().ok().expect("Failed parse");
            }
            self.buf_str.clear();
            self.reader
                .read_until(b'\n', &mut self.buf_str)
                .expect("Failed read");
            self.buf_iter = unsafe {
                let slice = str::from_utf8_unchecked(&self.buf_str);
                std::mem::transmute(slice.split_whitespace())
            }
        }
    }
}