#include "bits/stdc++.h"
#include "atcoder/all"
using namespace std;
using namespace atcoder;
using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
vector<int>to[200005];
void bfs(int n) {
	vector<int>d(n, INF);
	d[0] = 0;
	queue<int> q;
	q.emplace(0);
	while (!q.empty()) {
		int x = q.front();
		q.pop();
		for (auto v : to[x]) {
			if (d[v] > d[x] + 1) {
				d[v] = d[x] + 1;
				q.emplace(v);
			}
		}
	}
	if (INF == d[n - 1]) d[n - 1] = -1;
	cout << d[n - 1] << endl;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	rep(i, m) {
		int a, b; cin >> a >> b; a--; b--;
		to[a].push_back(b);
		to[b].push_back(a);
	}
	bfs(n);
	return 0;
}