#include<bits/stdc++.h> 
#define ll long long 
#define LL __int128_t 
#define PB push_back
#define MK make_pair
#define fi first
#define se second
#define FOR(i, x, y) for (decay<decltype(y)>::type i = (x), _##i = (y); i <= _##i; ++i)
#define FORD(i, x, y) for (decay<decltype(x)>::type i = (x), _##i = (y); i >= _##i; --i)
#define debug(x) cout<< "\033 -> "<<#x<<": "<<x<<endl
using namespace std;
const int N(100005);
vector<int> e[N];
int vis[N], dis[N];
int main() 
{ 
//	freopen("1.in","r",stdin); 
	ios::sync_with_stdio(false); 
	cin.tie(NULL);
	int n, m; cin >> n >> m;
	FOR(i, 1, m)
	{
		int x, y; cin >> x >> y;
		e[x].PB(y), e[y].PB(x);
	}
	queue<int> q; q.push(1); vis[1] = 1;
	while(!q.empty())
	{
		int x = q.front(); q.pop();
		if(x == n) break;
		for(auto &to : e[x]) if(!vis[to])
		{
			q.push(to);
			dis[to] = dis[x] + 1;
		}
	}
	cout<<dis[n]-1<<endl;
	return 0; 
}