#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,m;
  cin>>n>>m;
  int a[m],b[m];
  vector<vector<int>> g(n);
  for(int i = 0;i < m;i++){
    cin>>a[i]>>b[i];
    a[i]--;
    b[i]--;
    g[a[i]].push_back(b[i]);
    g[b[i]].push_back(a[i]);
  }
  queue<int> q;
  q.push(0);
  vector<int> cost(n,1000000);
  cost[0] = 0;
  while(!q.empty()){
    int nn = q.front();
    q.pop();
    for(int x:g[nn]){
      if(cost[x] == 1000000){
        q.push(x);
        cost[x] = cost[nn]+1;
      }
    }
  }
  if(cost[n-1] == 1000000){
    cout<<-1<<endl;
  }
  else{
  cout<<cost[n-1]<<endl;
  }
}