#include <bits/stdc++.h>
using namespace std;
const int INF = 100000000;
int main() {
    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);
    }
    queue<int> q;
    q.push(0);
    vector<int> dist1(N, INF);
    dist1[0] = 0;
    while (!q.empty()) {
        int now = q.front();
        q.pop();
        for (auto next : G[now]) {
            if (dist1[next] == INF) {
                q.push(next);
                dist1[next] = dist1[now] + 1;
            }
        }
    }
    q.push(N - 2);
    vector<int> dist2(N, INF);
    dist2[N - 2] = 0;
    while (!q.empty()) {
        int now = q.front();
        q.pop();
        for (auto next : G[now]) {
            if (dist2[next] == INF) {
                q.push(next);
                dist2[next] = dist2[now] + 1;
            }
        }
    }
    q.push(N - 1);
    vector<int> dist3(N, INF);
    dist3[N - 1] = 0;
    while (!q.empty()) {
        int now = q.front();
        q.pop();
        for (auto next : G[now]) {
            if (dist3[next] == INF) {
                q.push(next);
                dist3[next] = dist3[now] + 1;
            }
        }
    }
    int ans = dist1[N - 2] + dist2[N - 1] + dist3[0];
    ans = min(ans, dist1[N - 1] + dist3[N - 2] + dist2[0]);
    if (ans < INF) {
        cout << ans << endl;
    } else {
        cout << -1 << endl;
    }
}