// コンパイルはctrl + shift + B
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define all(x) (x).begin(), (x).end()
#define yes "Yes"
#define no "No"

// 最大公約数　O(log(N))
template<typename T>
T gcd(T a, T b) {
    if (b == 0) return a;
    else return gcd(b, a % b);
}

// 素数判定　O(sqrt(N))
bool is_prime(ll n) {
    for (ll i = 2; i*i <= n; i++) {
        if (n % i == 0) return false;
    }
    return true;
}

//n以下の素数求めマシーン　O(Nloglog(N))
vector<ll> getprime(ll n) {
    vector<ll> ans;
    vector<bool> isprime(n + 1, true);
    //0, 1はダメ
    isprime[0] = false; isprime[1] = false;

    //やる
    for (int i = 2; i <= n; i++) {
        if (!isprime[i]) continue;
        ans.push_back(i);

        for (int j =  2 * i; j <= n; j += i) {
            //i以外のiの倍数をキャンセル
            isprime[j] = false;
        }
    }
    return ans;
}

// nを素因数分解　O(sqrt(N))
vector<pair<ll, ll>> prime_factorize(ll n) {
    vector<pair<ll, ll>> ans;
    for (ll i = 2; i*i <= n; i++) {
        if (n % i != 0) continue;
        ll e = 0;
        while (n % i == 0) {
            e++;
            n /= i;
        }
        ans.push_back({i, e});
    }
    if (n != 1) ans.push_back({n, 1});
    return ans;
}

// 各n以下の最小の素因数　O(NlogN)
vector<ll> smallest_prime(ll n) {
    vector<ll> spf(n+1);
    for (ll i = 0; i <= n; i++) spf[i] = i; //初期化
    for (ll i = 2; i+i <= n; i++) {
        if (spf[i] == i) {
            for (ll j = i*i; j <= n; j += i) {
                if (spf[j] == j) spf[j] = i;
            }
        }
    }
    return spf;
}

// 以下、コードを記すのである。

// using mint = modint998244353;
using mint = modint1000000007;

int main() {
    int n, m; cin >> n >> m;
    vector<vector<int>> e(n);
    for (int i = 0; i < m; i++) {
        int u, v; cin >> u >> v;
        u--; v--;
        e[u].push_back(v);
    }
    ll INF = 1e18;
    vector<ll> iki(n, INF);
    iki[0] = 0;
    queue<int> q;
    q.push(0);
    vector<bool> seen(n);
    seen[0] = true;
    while (q.size()) {
        int u = q.front(); q.pop();
        for (auto v : e[u]) {
            if (seen[v]) continue;
            seen[v] = true;
            iki[v] = iki[u] + 1;
            q.push(v);
        }
    }
    bool a = seen[n-2];
    bool b = seen[n-1];
    int ans = -1;
    if (a) {
        bool f = true;
        int now = iki[n-2];
        q.push(n-2);
        vector<bool> seen(n);
        seen[n-2] = true;
        vector<int> d(n);
        while (q.size()) {
            int u = q.front(); q.pop();
            for (auto v : e[u]) {
                if (seen[v]) continue;
                seen[v] = true;
                d[v] = d[u] + 1;
                q.push(v);
            }
        }
        if (seen[n-1]) now += d[n-1];
        else f = false;
        q.push(n-1);
        vector<bool> seen1(n);
        seen[n-1] = true;
        vector<int> d1(n);
        while (q.size()) {
            int u = q.front(); q.pop();
            for (auto v : e[u]) {
                if (seen1[v]) continue;
                seen1[v] = true;
                d1[v] = d1[u] + 1;
                q.push(v);
            }
        }
        if (seen1[0]) now += d1[0];
        else f = false;    
        if (f) ans = now;
    }
    if (b) {
        bool f = true;
        int now = iki[n-1];
        q.push(n-1);
        vector<bool> seen(n);
        seen[n-1] = true;
        vector<int> di(n);
        while (q.size()) {
            int u = q.front(); q.pop();
            for (auto v : e[u]) {
                if (seen[v]) continue;
                seen[v] = true;
                di[v] = di[u] + 1;
                q.push(v);
            }
        }
        if (seen[n-2]) now += di[n-2];
        else f = false;
        q.push(n-2);
        vector<bool> seen1(n);
        seen[n-2] = true;
        vector<int> di1(n);
        while (q.size()) {
            int u = q.front(); q.pop();
            for (auto v : e[u]) {
                if (seen1[v]) continue;
                seen1[v] = true;
                di1[v] = di1[u] + 1;
                q.push(v);
            }
        }
        if (seen1[0]) now += di1[0];
        else f = false;     
        if (f) {
            if (ans < 0) ans = now;
            else ans = min(ans, now);
        }
    }
    cout << ans << endl;
    
}