/*
Author : Chandan Agrawal
College : Poornima College of Engg. jaipur, Raj
Mail : chandanagrawal23@gmail.com
" when you are not practicing someone else is ,
and the day u meet them u will lose "
*/
#include<bits/stdc++.h>
#include<stdio.h>
using namespace std;
#define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define MAX 200050
#define ll long long
#define ld long double
#define lli long long int
#define pb push_back
#define INF 1000000000000
#define mod 1000000007
// trignometric function always give value in Radians only
#define PI acos(-1) //3.1415926535897932384626433832795028
#define dsin(degree) sin(degree*(PI/180.0))
#define dcos(degree) cos(degree*(PI/180.0))
#define dtan(degree) tan(degree*(PI/180.0))
#define rsin(radian) sin(radian)
#define rcos(radian) cos(radian)
#define rtan(radian) tan(radian)
#define mem0(a) memset(a,0,sizeof(a))
#define mem1(a) memset(a,-1,sizeof(a))
#define memf(a) memset(a,false,sizeof(a))
#define loop(i,n) for (lli i = 0; i < n; i++)
#define FOR(i,a,b) for (lli i = a; i < b; i+=1)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define sz(x) int(x.size())
#define F first
#define S second
#define mii map<lli,lli>
#define mci map<char,lli>
#define vi vector<lli>
#define vbool vector<bool>
#define seti set<lli>
#define pii pair<lli,lli>
#define pcc pair<char,char>
#define gcd(a,b) __gcd((a),(b))
#define lcm(a,b) (a/gcd(a,b))*b
#define abs(x) ((x < 0)?-(x):x)
#define endl '\n'
template <typename T>
void print(T x){cout<<x<<endl;}
template <typename T1, typename T2>
void print2(T1 x,T2 y){cout<<x<<" "<<y<<endl;}
template <typename T1, typename T2,typename T3>
void print3(T1 x, T2 y,T3 z){cout<<x<<" "<<y<<" "<<z<<endl;}
#define scanarr(a,n) for(lli i=0;i<n;i++) cin>>a[i];
#define scanvec(a,n) for(lli i=0;i<n;i++){ lli x ; cin>>x; a.pb(x);}
#define printarr(a,n) for(lli i=0;i<n;i++) cout<<a[i]<<" "; cout<<endl;
#define printvec(vec) for(auto xt : vec) cout<<xt<<" "; cout<<"\n";
#define FD(N) fixed<<setprecision(N)
#define deb(x) cout<<#x<<" "<<x<<endl;
// chandan1,2
void chandan1(){int y=1;return;}
void chandan2(){
loop(i,10){
lli x=1;
}
return(chandan1());
}
lli dist[MAX];
lli parent[MAX];
int vis[MAX];
vi adj[MAX];
void dfs(lli src , lli lvl)
{
vis[src]=1;
dist[src] = lvl;
for(auto xt : adj[src])
{
if(!vis[xt])
{
parent[xt] = src;
dfs(xt , lvl+1);
}
else
{
if(dist[xt] < dist[src]+1)
{
dist[xt] = dist[src]+1;
parent[xt] = src;
}
}
}
}
int main(){
fastio
lli t=1;
//cin>>t;
chandan2();
while(t--) {
lli n,m;
cin>>n>>m;
loop(i,m)
{
lli x,y;
cin>>x>>y;
adj[x].pb(y);
}
dfs(1,0);
if(dist[n]==0)
print("IMPOSSIBLE");
else
{
vi ans;
ans.pb(n);
while(n!=1)
{
n = parent[n];
ans.pb(n);
}
reverse(all(ans));
print(sz(ans));
printvec(ans);
}
}
return 0;
}
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