#include<iostream>
#include<vector>
#include<queue>
using namespace std;
using ll=long long;
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
template<class T> bool chmax(T &a, T b){if (a < b){a = b;return true;} else return false;}
template<class T> bool chmin(T &a, T b){if (a > b){a = b;return true;} else return false;}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N,M;
    cin>>N>>M;
    vector<vector<int>>g(N);
    rep(i,M){
        int a,b;
        cin>>a>>b;
        a--;
        b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    vector<int>d(N,1<<30);
    d[0]=0;
    queue<pair<int,int>>q;
    q.push(make_pair(0,0));
    while(q.size()){
        auto[c,x]=q.front();
        q.pop();
        for(auto i:g[x]){
            if(chmin(d[i],c+1))q.push(make_pair(d[i],i));
        }
    }
    if(d[N-1]==1<<30)cout<<-1<<"\n";
    else cout<<d[N-1]<<"\n";
}