#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

int main() {
    int n, m; cin >> n >> m;

    auto g = vec<int>(uns, n, 0);
    for (int i = 0; i < m; ++i) {
        int a, b; cin >> a >> b; --a; --b;
        g[a].push_back(b);
        g[b].push_back(a);
    }

    queue<int> que;
    auto dist = vec<int>(-1, n);

    que.push(0);
    dist[0] = 0;
    while (!empty(que)) {
        auto v = que.front(); que.pop();

        for (auto u : g[v]) {
            if (dist[u] != -1) {
                continue;
            }
            dist[u] = dist[v] + 1;
            que.push(u);
        }
    }

    cout << dist[n - 1] << endl;
}