#include <bits/stdc++.h>
template<class T> inline bool chmin(T&a, T b){if(a > b){a = b; return true;}else{return false;}}
template<class T> inline bool chmax(T&a, T b){if(a < b){a = b; return true;}else{return false;}}
#define ll long long
#define double long double
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for(int i=1;i<=(n);i++)
#define mod (ll)(1e9+7)
#define inf (ll)(3e18+7)
#define eps (double)(1e-9)
#define pi (double) acos(-1)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
using namespace std;

using Graph = vector<vector<int>>;

int main(){
    int n, m;
    cin >> n >> m;
    Graph 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);
    d[0] = 0;
    queue<int> que;
    que.push(0);
    while(!que.empty()){
        int v = que.front();
        que.pop();
        for(auto nv : G[v]){
            if(d[nv] == -1){
                d[nv] = d[v] + 1;
                que.push(nv);
            }
        }
    }
    cout << d[n-1] << endl;
}