Shared code

//Problem Link - 
/* By Shark08*/
#include<bits/stdc++.h>
/*#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include<ext/pb_ds/trie_policy.hpp>*/
// using namespace __gnu_pbds;
using namespace std;
 
#define ll                  long long int
#define ld                  long double 
#define mod                 1000000007
#define inf                 1e9
#define endl                "\n"
#define pb                  push_back
#define vi                  vector<ll>
#define vs                  vector<ss>
#define pii                 pair<ll,ll>
#define ump                 unordered_map
#define mp                  make_pair 
#define pq_max              priority_queue<ll,ll>
#define pq_min              priority_queue<ll,vector<ll>,greater<ll> >
#define all(v)              v.begin(),v.end()
#define ff                  first
#define ss                  second
#define mid(l,r)            (l+(r-l)/2)
#define bitc(x)             __buildtin_popcount(x)
#define loop(i,a,b)         for(int i=a ; i<=b ; i++)
#define looprev(i,a,b)      for(int i=a;i>=b;i--)
#define iter(c,it)          for(__typeof(c.begin()) it =c.begin() ; it!=c.end();it++)
#define log(args...)        {string _s = #args; replace(_s.begin(), _s.end(), ',',' ' ); stringstream __ss(_s); istream_iterator<string> _it(__ss) ; err(_it, args); }      
#define logarr(arr,a,b)     for(int z=a;z<=b;z++) cout<<(arr[z])<<" "; cout<<endl;
template<typename T> T gcd(T a, T b){ if(a%b) return gcd(b, a%b) ; return b;}
template<typename T> T lcm(T a ,T b) { return (a*(b/gcd(a,b)));}
 
void err(istream_iterator<string> it){}
template <typename T,typename... Args>
void err (istream_iterator<string> it, T a, Args... args){
    cout<< *it <<" = "<< a << endl;
    err(++it,args...);
}
//
//
 
void file_i_o()
{    
    ios_base::sync_with_stdio(false);
    //untie
    cin.tie(0);
    cout.tie(0);
    #ifndef ONLINE_JUDGE
        freopen("input.txt","r",stdin);
        freopen("output.txt","w",stdout);
    #endif
}
const int N =1e6;
vector<vector<ll>> Adj(N,vector<ll>());
vector<ll> Par(N,-1);
vector<ll> Deg(N,0);
 
void topo(queue<ll> &Q)
{
    while(!Q.empty())
    {
        int x = Q.front();
        Q.pop();
 
        for(ll t : Adj[x])
        {
            Deg[t]--;
            if(Deg[t] == 0)
            {   
                Par[t] = x;
                if(t != 1)
                {
                    Q.push(t);
                }
                
            }
        }
    }
}
 
int main(int argc, char const *argv[])
{
    /* code */
    clock_t begin = clock();
    file_i_o();
    ll n,m;
    cin>>n>>m;
    ll a,b;
    for(ll i= 1; i<=n ; i++)
    {
        Deg[i] = 0;
        Par[i] =-1;
    }
    loop(i,0,m-1)
    {
        cin>>a>>b;
        Adj[a].pb(b);
        Deg[b]++;
    }
 
 
 
    queue<ll> Q;
    for(ll i= 2; i<=n;i++)
    {
        if(Deg[i] == 0)
        {
            Q.push(i);
        }
    }
    topo(Q);
    Q.push(1);
    Par[n] = -1;
    Par[1] = -1;
    topo(Q);
 
    if(Par[n] == -1)
    {
        cout<<"IMPOSSIBLE";
    }
    else
    {
        ll cur = n;
        vector<ll> Ans;
        while(Par[cur] != -1)
        {
            Ans.push_back(cur);
            cur = Par[cur];
        }
        Ans.push_back(1);
        cout<<Ans.size()<<endl;
        reverse(Ans.begin(),Ans.end());
        loop(i,0,Ans.size()-1)
        {
            cout<<Ans[i]<<" ";
        }
    }
 
    #ifndef ONLINE_JUDGE
        clock_t end= clock();
        cout<<"\n\n\nExecuted In:"<< double(end-begin)/CLOCKS_PER_SEC*1000<<" ms";
    #endif
    return 0;
}