code

#include <bits/stdc++.h>
using namespace std;
#define X ios_base::sync_with_stdio(false); cin.tie(NULL);
#define FIXED_FLOAT(x) std::fixed <<std::setprecision(2)<<(x)


void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif


// long long p = 1e9+7;

typedef long long ll;
typedef pair<ll,ll> pl;
typedef vector<int> VI;
typedef vector<pair<ll,ll>> VP;
typedef vector<ll> VL;
typedef vector<bool> VB;

// typedef pair<ll, ll> PL;
typedef unordered_map<ll, ll> UMP;
#define FOR(i,b) for(i=0;i<b;i++)
#define pb push_back
#define mp make_pair

// typedef  unordered_set<ll>;


void printa(VI &x,ll n){
    ll i;
    FOR(i, n){
        cout<<x[i]<<" ";
    }
    cout<<endl;
}


/////GLOABLS VARS
ll MOD = 1e9+7;
ll gmx = 1e5+7;
VL fact(gmx, 1);
//////FUNCTIONS
// ll pow(ll val, ll deg)
// {
//     if (!deg)
//         return 1 % MOD;
//     if (deg & 1)
//         return pow(val, deg - 1) * val % MOD;
//     ll res = pow(val, deg >> 1);
//     return (res * res) % MOD;
// }
ll powm(ll a, ll p) {
    ll res = 1;
    while(p) {
        if(p & 1) {res = (res * a) % MOD;}
        p /= 2;
        a = (a * a) % MOD;
    }
    return res;
}
ll inv(ll r){
    return powm(r, MOD-2)%MOD;
}
ll nCr(ll n, ll r){
    ll tmp = fact[n-r]*fact[r];
    tmp = tmp%MOD;
    return (fact[n]*inv(tmp))%MOD;
}


int main(){
      ios::sync_with_stdio(0);
      cin.tie(0);
    #ifndef ONLINE_JUDGE
        freopen("test_input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
        #define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
    #endif
    ll i,u,v,j,c;
    ll n,m;
    cin>>n>>m;
    vector<VL> adj(n+1);
    FOR(i,m){
        cin>>u>>v;
        adj[u].pb(v);
    }
    VL dist(n+1, -1);
    VL pre(n+1, -1);
    dist[1] = 0;
    debug(adj[1],n,m);
    queue <ll> q;
    q.push(1);
    while(q.size()>0){
        ll e = q.front();q.pop();
        // debug(e);
        for(auto nb: adj[e]){
            if(dist[nb]<dist[e]+1){
                dist[nb]  = dist[e]+1;
                pre[nb] = e;
                q.push(nb);
            }
        }
    }
    if(dist[n]==-1){
        cout<<"IMPOSSIBLE\n";
    }
    else{
        cout<<dist[n]+1<<'\n';
        ll node =n;
        VL tmp;
        while(node!=-1){
            tmp.pb(node);
            node = pre[node];
        }
        for(i=0;i<tmp.size();i++){
            cout<<tmp[tmp.size()-1-i]<<" ";
        }
    }


}