#include <iostream>
#include <stdio.h>
#include <vector>
#include <string.h>
#include <queue>
#define MAX 100002
using namespace std;
vector<int> vec[MAX];
int dist[MAX];
bool visited[MAX] = { 0, };
queue<int> q;
int main()
{
memset(dist, -1, sizeof(dist));
int n, m;
cin >> n >> m;
for (int i = 0; i < m; i++) {
int a, b;
cin >> a >> b; // 연결
a--; b--;
vec[a].push_back(b);
vec[b].push_back(a);
}
q.push(0);
visited[0] = true;
dist[0] = 0;
while (!q.empty()) {
int here = q.front();
q.pop();
for (int i = 0; i < vec[here].size(); i++) {
if (!visited[vec[here][i]]) {
visited[vec[here][i]] = true;
q.push(vec[here][i]);
dist[vec[here][i]] = dist[here] + 1;
}
}
}
cout << dist[n - 1] << endl;
return 0;
}
