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