#include<iostream>
#include<vector>
#include<ranges>
#include<queue>
using namespace std;
using ll = long long;

using Graph = vector<vector<int>>;

void bfs(Graph& G, int start, vector<ll>& dist) {
    dist[start] = 0;
    ll inf = 1e12;

    queue<int> que;
    que.push(start);

    while (!que.empty()) {
        auto cur_v = que.front();
        que.pop();
        for (auto next_v : G[cur_v]) {
            if (dist[next_v] != inf) {
                continue;
            }
            que.push(next_v);
            dist[next_v] = dist[cur_v] + 1;
        }
    }
}

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

    ll inf = 1e12;

    // 0 -> N - 1
    // N - 1 -> N
    // N -> 0

    // 0 -> N
    // N -> N - 1
    // N - 1 -> 0
    vector<vector<ll>> dists(3, vector(N, inf));

    bfs(G, 0, dists[0]);
    bfs(G, N - 2, dists[1]);
    bfs(G, N - 1, dists[2]);

    auto ans1 = dists[0][N - 2] + dists[1][N - 1] + dists[2][0];
    auto ans2 = dists[0][N - 1] + dists[2][N - 2] + dists[1][0];

    auto ans = min(ans1, ans2);
    if (ans >= inf) {
        cout << -1 << endl;
    } else {
        cout << ans << endl;
    }
}