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

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

    vector<int> d(N, -1);
    d[0] = 0;
    queue<int> que;
    que.push(0);
    while (!que.empty()) {
        int u = que.front();
        que.pop();

        for (int v : G[u]) {
            if (d[v] == -1) {
                d[v] = d[u] + 1;
                que.push(v);
            }
        }
    }

    cout << d[N - 1] << endl;

    return 0;
}