#include <iostream>
#include <fstream>
#include <stack>
using namespace std;
ifstream fin("euler.in");
ofstream fout("euler.out");
int x[2005][2005],n,L[20005],p=0;

void citire(){
    int i,j,l;
    fin >>n;
    while(fin.peek()!=EOF){
        fin>>i>>j;
        x[i][j]=x[j][i]=1;
    }
}
void afisare(){
    int i,j;
    for(i=1;i<=n;i++){
        for(j=1;j<=n;j++) cout << x[i][j] << " ";
        cout << " \n";
    }
}
void Euler(int k){
for(int i=1;i<=n;i++)
if(x[k][i]==1){
    x[k][i]=x[i][k]=0;
    Euler(i);
}
L[++p]=k;
}
int main(){
citire();
Euler(1);
fout << p << "\n";
for(int i=p;i>=1;i--) fout << L[i]<< " ";
return 0;
}