#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#define rep(i, n) for(i = 0; i < n; i++)
using namespace std;

int n, m;
vector<int> et[200000];
int dist[200000];

int main() {
	int i;
	
	cin >> n >> m;
	rep(i, m) {
		int a, b;
		cin >> a >> b; a--; b--;
		et[a].push_back(b);
		et[b].push_back(a);
	}
	rep(i, n) dist[i] = -1;
	
	queue<int> que;
	que.push(0);
	dist[0] = 0;
	while (!que.empty()) {
		int v = que.front(); que.pop();
		rep(i, et[v].size()) {
			int nv = et[v][i];
			if (dist[nv] == -1) {
				dist[nv] = dist[v] + 1;
				que.push(nv);
			}
		}
	}
	
	cout << dist[n - 1] << endl;
	return 0;
}