#include<fstream>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n,m,x,y,a[201][201],v[20100],ok,p=1;
void citire()
{
    f>>n;
    while(f>>x>>y)
        if(a[x][y]==0)
        {
            m++;
            a[x][y]=a[y][x]=1;
        }
}
bool verif(int k)
{
    if(a[v[k]][v[k-1]]<1) return false;
    return true;
}
void bt(int k)
{
    if(k==m+2 and v[k-1]==true) ok=1;
    else
        for(int i=1;i<=n and ok==0;++i)
    {
        v[k]=i;
        if(verif(k))
        {
                a[v[k]][v[k-1]]=a[v[k-1]][v[k]]=-1;
                bt(k+1);
                 a[v[k]][v[k-1]]=a[v[k-1]][v[k]]=1;
        }
    }
}
int main()
{
    citire();
    v[1]=1;
    bt(2);g<<m+1<<endl;
    for(int i=1;i<=m+1;++i)
        g<<v[i]<<" ";


}