#include <bits/stdc++.h>

using namespace std;

void fast_io() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}
const int INF = 5e8;
vector<int> calc_dist(int s, vector<vector<int>> &g) {
    int n = g.size();
    vector<int> dist(n, INF);
    dist[s] = 0;
    deque<int> que;
    que.push_back(s);
    while (!que.empty()) {
        int v = que.front();
        que.pop_front();
        for (int u : g[v]) {
            if (dist[u] == INF) {
                dist[u] = dist[v] + 1;
                que.push_back(u);
            }
        }
    }
    return dist;
}
int main() {
    fast_io();
    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);
    }
    auto dist_0 = calc_dist(0, g);
    auto dist_n1 = calc_dist(n - 2, g);
    auto dist_n = calc_dist(n - 1, g);
    int ans = min(dist_0[n - 2] + dist_n1[n - 1] + dist_n[0],
                  dist_0[n - 1] + dist_n[n - 2] + dist_n1[0]);
    if (ans > INF) {
        cout << -1 << endl;
    } else {
        cout << ans << endl;
    }
}