#include <iostream>
#include <fstream>
#include <bitset>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <algorithm>
#include <stack>
using namespace std;
vector <int>nd[110001];
stack <int> Q;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
inline bool verificare(int n)
{   int i;
    for( i=1;i<=n;i++)
    {
        if(nd[i].size()&1) return 0;

    }
    return 1;
}
int main()
{
    int n,m,x,i=1,y;
    fin>>n>>m;
    while(i<=m)
    {   fin>>x>>y;
        nd[x].push_back(y);
        nd[y].push_back(x);
        i++;
    }
    if(!verificare(n)) fout<<-1;
    else
    {
    Q.push(1);
    int p,u;
    while(1)
    {
        while(nd[Q.top()].size()&&Q.size()<=m)
        {   fout<<Q.top()<<" ";
            p=nd[Q.top()].back();
            u=Q.top();
            nd[Q.top()].pop_back();
            Q.push(p);
            nd[p].erase(find(nd[p].begin(),nd[p].end(),u));
        }
        while(!nd[Q.top()].size())
        {
            Q.pop();
            if(!Q.size()) break;
        }
        if(!Q.size()||Q.size()==m+1) break;
    }
    }
}