#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
typedef long long ll;
using namespace std;

struct edge {
    int to;
    int cost;
};
using P = pair<int, int>;
vector<vector<edge>> G;
vector<int> d;
void dijkstra(int s) {
    priority_queue<P, vector<P>, greater<P>> que;
    fill(d.begin(), d.end(), 1e9);
    d[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
        P p = que.top();
        que.pop();
        int v = p.second;
        if (d[v] < p.first)
            continue;
        rep(i, G[v].size()) {
            edge e = G[v][i];
            if (d[e.to] > d[v] + e.cost) {
                d[e.to] = d[v] + e.cost;
                que.push(P(d[e.to], e.to));
            }
        }
    }
}

int main() {
    int N, M;
    cin >> N >> M;
    G.resize(N);
    d.resize(N);
    rep(i, M) {
        int a, b;
        cin >> a >> b;
        a--, b--;
        G[a].push_back({b, 1});
        G[b].push_back({a, 1});
    }

    dijkstra(0);

    if (d[N - 1] == 1e9) d[N - 1] = -1;
    cout << d[N - 1] << endl;

    return 0;
}