#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
template<typename T> using pq = priority_queue<T>;
template<typename T> using pq_g = priority_queue<T, vector<T>, greater<T>>;
using mint = modint998244353;
// using mint = modint1000000007;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define NP next_permutation
#define debug(x) cerr << #x << " = " << (x) << endl
const int INF = 2e9;
const ll LINF = 2e18;
const ll mod = 998244353;
// const ll mod = 1000000007;
void Yes(bool a) {cout << (a ? "Yes" : "No") << endl;}
void YES(bool a) {cout << (a ? "YES" : "NO") << endl;}
void Possible(bool a) {cout << (a ? "Possible" : "Impossible") << endl;}
void POSSIBLE(bool a) {cout << (a ? "POSSIBLE" : "IMPOSSIBLE") << endl;}
template<typename T> void vcin(vector<T> &a) {rep(i, int(a.size())) cin >> a[i];}
template<typename T, typename K> void vcin(vector<T> &a, vector<K> &b) {rep(i, int(a.size())) cin >> a[i] >> b[i];}
template<typename T> void vcout(vector<T> &a) {rep(i, int(a.size())) {cout << a[i] << " ";} cout << endl;}
template<typename T> void vcin(vector<vector<T>> &a) {rep(i, int(a.size())) rep(j, (int)a[i].size()) cin >> a[i][j];}
template<typename T> void vcout(vector<vector<T>> &a) {rep(i, int(a.size())) {rep(j, int(a[i].size())) {cout << a[i][j] << " ";} cout << endl;} cout << endl;}
template<typename T> auto vmin(vector<T> &a) {return *min_element(all(a));}
template<typename T> auto vmax(vector<T> &a) {return *max_element(all(a));}
template<typename T> auto vsum(vector<T> a) {return accumulate(all(a), T(0));}
template<typename T> bool chmin(T &a, T b){if(a > b){a = b; return true;} return false;}
template<typename T> bool chmax(T &a, T b){if(a < b){a = b; return true;} return false;}

void cincout() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
}
 
int main() {
    cincout();

    int N, M;
    cin >> N >> M;
    
    vector<vector<int>> G(N);
    for (int i = 0; i < M; i++) {
        int u, v;
        cin >> u >> v;
        u--, v--;
        G[u].push_back(v);
    }

    vector<vector<int>> dist(N, vector<int>(4, INF));
    dist[0][0] = 0;
    queue<pair<int, int>> q;
    q.push({0, 0});

    while (!q.empty()) {
        auto [v, bit] = q.front();
        q.pop();

        for (int &next_v : G[v]) {
            if (next_v == N - 2) {
                if (chmin(dist[next_v][bit | 1], dist[v][bit] + 1)) q.push({next_v, bit | 1});
            }

            else if (next_v == N - 1) {
                if (chmin(dist[next_v][bit | 2], dist[v][bit] + 1)) q.push({next_v, bit | 2});
            }

            else {
                if (chmin(dist[next_v][bit], dist[v][bit] + 1)) q.push({next_v, bit});
            }
        }
    }

    cout << (dist[0][3] != INF ? dist[0][3] : -1) << endl;
}