#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<vector<int>> E(N);
  for (int i = 0; i < M; i++){
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    E[a].push_back(b);
    E[b].push_back(a);
  }
  vector<int> d(N, -1);
  d[0] = 0;
  queue<int> Q;
  Q.push(0);
  while (!Q.empty()){
    int v = Q.front();
    Q.pop();
    for (int w : E[v]){
      if (d[w] == -1){
        d[w] = d[v] + 1;
        Q.push(w);
      }
    }
  }
  cout << d[N - 1] << endl;
}