#include <bits/stdc++.h>
using namespace std;

int 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;
        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 pos = q.front();
        q.pop();
        for(int x:G[pos]){
            if(dist[x] != -1) continue;
            q.push(x);
            dist[x] = dist[pos] + 1;
        }
    }
    cout<<dist[N-1]<<endl;
}