#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

using mint = modint998244353;

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

ll my_pow(ll x, ll n, ll mod) {
    // 　繰り返し二乗法．x^nをmodで割った余り．
    ll ret;
    if (n == 0) {
        ret = 1;
    } else if (n % 2 == 1) {
        ret = (x * my_pow((x * x) % mod, n / 2, mod)) % mod;
    } else {
        ret = my_pow((x * x) % mod, n / 2, mod);
    }
    return ret;
}

ll inv(ll x, ll mod) { return my_pow(x, mod - 2, mod); }

vector<int> bfs(vector<vector<int>> &graph, int v, int N) {
    int INF = 4 * N + 3;
    vector<int> dis(N, INF);
    queue<int> que;
    vector<int> isvisited(N, false);
    dis[v] = 0;
    isvisited[v] = true;
    que.push(v);
    while (que.size()) {
        int p = que.front();
        que.pop();
        for (int x : graph[p]) {
            if (isvisited[x]) {
                continue;
            }
            isvisited[x] = true;
            dis[x] = dis[p] + 1;
            que.push(x);
        }
    }
    return dis;
}

int main() {
    int N, M;
    cin >> N >> M;
    assert(3 <= N && N <= 100000);
    int min_m;
    if (N >= 1000) {
        min_m = 100000;
    } else {
        min_m = min(100000, N * (N - 1));
    }
    assert(0 <= M && M <= min_m);
    vector<vector<int>> graph(N, vector<int>(0));
    vector<int> u(M);
    vector<int> v(M);
    map<pii, int> mp;
    for (int i = 0; i < M; i++) {
        cin >> u[i] >> v[i];
        assert(1 <= u[i] && u[i] <= N);
        assert(1 <= v[i] && v[i] <= N);
        u[i]--;
        v[i]--;
        graph[u[i]].push_back(v[i]);
        assert(u[i] != v[i]);
        assert(mp[pii(u[i], v[i])] == 0);
        mp[pii(u[i], v[i])]++;
    }
    int INF = 4 * N + 2;
    vector<int> dist1 = bfs(graph, 0, N);
    vector<int> distn1 = bfs(graph, N - 2, N);
    vector<int> distn = bfs(graph, N - 1, N);
    // debug(dist1);

    // 1 -> n - 1 -> n -> 1
    int ans1 = dist1[N - 2] + distn1[N - 1] + distn[0];
    // 1 -> n -> n - 1 -> 1
    int ans2 = dist1[N - 1] + distn[N - 2] + distn1[0];
    int ans = min(ans1, ans2);
    if (ans >= INF) {
        cout << -1 << endl;
    } else {
        cout << ans << endl;
    }
}