#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define rrep(i, n) for (int i = n - 1; i >= 0; i--)
#define rrep1(i, n) for (int i = n; i >= 1; i--)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define eb emplace_back
#define fi first
#define se second
#define sz(x) (int)(x).size()
template <class T> using V = vector<T>;
template <class T> using VV = V<V<T>>;
typedef long long int ll;

void speedUpIO() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
}

template <class T> bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template <class T> bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
/*--------------------------------------------------*/
typedef pair<int, int> P;

const int INF = 1e9;
const ll LINF = 1e18;
const int MX = 100010;

void solve() {
    ll n, m;
    cin >> n >> m;
    VV<ll> G(n);
    rep(i, m) {
        ll a, b;
        cin >> a >> b;
        a--, b--;
        G[a].eb(b);
    }
    auto bfs = [&](ll s, ll g) -> ll {
        V<ll> dist(n, LINF);
        queue<ll> Q;
        dist[s] = 0;
        Q.emplace(s);
        while (!Q.empty()) {
            ll v = Q.front();
            Q.pop();
            for (ll u : G[v]) {
                if (dist[u] != LINF) continue;
                dist[u] = dist[v] + 1;
                Q.emplace(u);
            }
        }
        return dist[g];
    };
    ll ans = LINF;
    chmin(ans, bfs(0, n - 2) + bfs(n - 2, n - 1) + bfs(n - 1, 0));
    chmin(ans, bfs(0, n - 1) + bfs(n - 1, n - 2) + bfs(n - 2, 0));
    if (ans == LINF) ans = -1;
    cout << ans << "\n";
}

int main() {
    speedUpIO();
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
        // cout << solve() << "\n";
        // cout << (solve() ? "YES" : "NO") << "\n";
        // cout << fixed << setprecision(15) << solve() << "\n";
    }
    return 0;
}