#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using vl = vector<ll>;
using vb = vector<bool>;
using vc = vector<char>;
using vs = vector<string>;
using pll = pair<ll, ll>;
using vpl = vector<pll>;
#define pb push_back
#define fi first
#define se second
#define f(i, a, b) for (ll i = a; i <= b; i++)
#define fr(i, a, b) for (ll i = b; i >= a; i--)
#define sz(x) (ll) x.size()
#define debug(val) cerr << #val << " = " << val << '\n';
#define all(x) x.begin(), x.end()
const ll MOD = 1e9 + 7;
void bfs(ll start, vector<vl> &adj, vector<pll> &path) {
path[start] = {-1,1};
queue<ll> q;
q.push(start);
while (!q.empty()) {
ll u = q.front(); q.pop();
ll ct = path[u].se;
for (ll v: adj[u]) {
if (path[v] != pll{-1,-1}) continue;
path[v] = {u,ct+1};
q.push(v);
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// string name = "time";
// freopen((name + ".in").c_str(), "r", stdin);
// freopen((name + ".out").c_str(), "w", stdout);
// precompute
// vl dices = {1,2,3,4,5,6};
ll n,m;
cin >> n >> m;
vector<vl> adj(n+1);
vector<pll> path(n+1, pll({-1,-1}));
f(i,1,m) {
ll a,b;
cin >> a >> b;
adj[a].push_back(b),adj[b].push_back(a);
}
bfs(1,adj,path);
ll len = path[n].se;
if (len == -1) {
cout << "IMPOSSIBLE\n";
return 0;
}
// backtrack
vl path2(len);
ll i = len-1, u = n;
path2[i--] = n;
do {
u = path[u].fi;
path2[i--] = u;
} while (u != 1);
cout << len << "\n";
f(i,0,len-1) cout << path2[i] << " \n"[i==len-1];
}
